**EDIT** 14/06/2016 - A lot of the stuff here doesn't apply to Quake: Champions. It looks like a genuine attempt to me to bring Quake to the modern gaming culture, and I hope it is successful.
I see a lot of people on the internet think of the oldschool shooters as 'mindless' twitch FPS games that don't require any tactics. I've seen this in vods, trailers, twitch chat over the years and it got me thinking of why Quake doesn't exist in modern gaming culture.
When those people watch team games in Quake all they see is 'people shooting stuff'. However, at every LAN event I have been to over the years, and I have been to a lot of tournaments since the early 2000's for Q3 and Q4, most I have spoken to at the events who have never seen Quake played before were very impressed by the duelers when they were up on the big screen. At many events the duelers got the crowd cheering more than the CS and RTS games did, and many people I spoke to said they found watching Quake to be the best part of the tournament. Duel is the reason why Quake is considered the pinnacle of FPS skill by non-quakers who know what they are talking about.
And to be honest, CTF and TDM tactics aren't that advanced when you consider the bigger picture in Quake, it's more about acquired CTF/TDM mode experience and being able to instinctively and habitually work well with the other 3-4 players on the team without having to communicate the overall strategy because the gameplay is so fast paced that by the time one person articulates a strategy the opportunity to apply the in depth tactical routes / teamwork / maneuvers has already gone. It is chaotic, teammates are dieing and respawning constantly and being repositioned elsewhere throughout the whole game. Compare that to CS where the casters have a whole bunch of time to talk about the overall strategy and what is going on because the game is slow enough to allow it.
I would estimate that 70-80% of what goes on in a game of CTF or TDM is not recognised by a viewer who doesn't understand the complexities of Quake, whereas with Duel it is more noticeable and the casters have more time to explain what is happening and why.
There has been a few threads on ESR trying to say why Quake has failed, Disrepute tried to blame the focus on duel as the reason, others say it's iDsoftware's fault, but so far everyone is only peeling one side off the methaphorical 'banana' that is 'why quake failed.' It's more complex than what has been discussed so far. Tennis for example shows that a 1v1 sport can be very successful where the top percentage of players in the world make an extremely good living off playing from travelling around the world competing in grand slams and smaller tournaments, and the grand slams are watched by millions of people.
So I sat down and tried to reason through why Quake has failed and get to the core reason why, and came up with the following summaries:
Increased popularity of the gaming industry: It is a fact that starting from the early 2000's most games that are massively popular are dumbed down to make them more accessible to a wider range of audiences. The more popular something is, the easier and more friendly it is to lower skilled players. Quake in its current form just does not fit into the modern gaming culture because it demands dedication, skill, determination and most relevantly lots of time and practice to get to a high level. Quake is a game for people who are competitive, but the majority of the gaming culture just want to play games to have fun by themselves or with friends or waste time on something that makes them feel good.
Inept adaption by iDsoftware: iD failed to see the trends of popular gaming, or saw it and chose to ignore it. Instead of following the trends of modern FPS of dumbing down gameplay and make it more simple, introducing experience levelling, item unlocks, achievements, ladders, etc they released games like Quake4 and thought they could just repeat the same success they had with all of their flagship games before. By the time Q4 came out the whole culture of gaming had already changed dramatically in that it wasn't just a select few 'nerds' playing it at school any more. By the time Q4 came out there was already masses of casuals getting into gaming and with all the easier and more accessible alternatives to Quake4 that was out at the time it had no chance of drawing a large number of players.
Regulated official eSports oversight: there is no governing body that decides the rules and regulations of 'electronic sports'. Anyone can throw up a website, run a tournament, and call it esports. With real life sports, going back to tennis as an exmaple, you had set rules that have been in place for years and these rules are applied globally and controlled centrally for all official tournaments. Sports have a standard that must be met by tournaments, an official ATP tennis tournament cannot simply say 'we are going to dumb down the professional game of tennis by allowing a second ball bounce so we can get more participants and make more money,' however this is what has happened in 'esports' over the years. When you consider what is an 'electronic sport' skill, Quake is a timeless skill that still hasn't been matched today in any popular modern FPS games. With a more regulated eSports body that is honest and operates on integrity and focuses purely on the most skillful forms of 'electronic' sports, Quake may have seen more success than it did for a longer period of time.
Popular gaming culture and consumerism: With the advent of popular gaming culture comes big money, big companies and consumerism. A game like Quake was made in a era before gaming was part of everyones lives in popular culture. Some of the pressures of consumerism did not have as much of a part to play as it does now. Truely competitive gamer numbers pale in comparison to the casual market who are not competitive. If you are playing a game casually for the simple of reason of enjoyment and that 'new' feeling you get when you try a new game for the first time and you aren't interested in being competitive and practicing, you will run out of stuff to do very quickly in the pre-2000 era of gaming. Big publishers recognised this and this is when you started to see all of the bells and whistles come into a game like achievements, unlocks, experience levelling, etc (in FPS games, obviously RPG's had this formula already). Once a casual player has finally sunk hundreds of hours into their game to unlock all of the meaningless achievements a brand new game is already out again these days. Now they can do the same thing all over again. By the time 2008/2009 came around, iD finally caught on and attempted to modernise Q3 in the form of Quakelive, but it was executed poorly which resulted in large queue times on launch day, ineffective matchmaking and ranking, a tiny budget and bad marketing and decision making.
When you consider all of this, and what Quake's strong points are and why there is a dedicated small number of players who love it and recognise it for its brilliance, you will realise that Quake and popular gaming can't co-exist how we would want it. To make Quake popular today and played by hundreds of thousands or millions of players, you need to chop out the heart of Quake to the point that it won't even be recognisable as Quake any more.
I think there is nothing that could have been done to prevent Quake from losing its spot as the most popular competitive FPS while retaining the part of what makes Quake so good, given the trends of popular gaming culture and how it is driven by big publishers whose only goal is more $$$, however if a number of things were done differently by iDsoftware, community organisers and a couple of sponsors Quake could have still been a staple eletronic sport today, it wouldn't have had huge numbers of players, but a bracket of professionals that played on a year round circut similar to how tennis operates. Non-quakers enjoy watching Quake, just like people who have never played tennis enjoy watching the grand slams, because they can appreciate the masters and skill that the players have. I know many people who have played tennis maybe once or twice in their life, but still watch the grand slams. It could have been the same for Quake.
Quake demanded excellence, honesty and professionalism in a culture and industry of mediocrity, laziness and greed. I think that it's too late to change anything now, unfortunately.