I'm a huge Quake fan. I've been playing nearly every day for over a decade. It's difficult to imagine an IP that has been managed quite as poorly as Quake has.
The beginning of the end was Quake Live. QL was a fantastic product: In the beginning, it was essentially a free version of Q3A with a large number of QoL tweaks that ran in your browser. However, from the start it had trouble making money. As mentioned, QL was free, but you could pay extra for the ability to host your own games using id's servers. This monetization model continued for a surprisingly long time despite id admitting that QL was losing them money. The player base was never huge, but it was big enough that you could generally find a game at all hours of the day if you were in a popular enough region. QL's population slowly dwindled, however, and a highly bungled Steam launch - complete with changes nobody asked for intended to make the game easier - merely accelerated the process.
QL's development history is typified by inaction and ignorance of the player base. Id failed to capitalize in any meaningful way on the value of rebooting and offering for free what is arguably the strongest game in id's stellar lineup. Instead of looking at what other games were doing with matchmaking to address the very real concern that QL's largest negative to new players was that you were virtually guaranteed to get slaughtered by experienced players for months if not longer before getting a W, QL tried to encourage the player base to play the game with different rules that they supposed would be more welcoming to new players. Of course, this didn't work; QL's fanbase inexplicably liked the game as it was and they weren't interested in features like loadouts and item pickup timers.
QL is actually still alive, but the player base never truly recovered from the transition to Steam and id continues to be content to let it languish instead of taking advantage of the recent trend of old games being revived.
The story of Quake Champions is similar. QC started out with a lot of ill will because of its dubious premise - let's make Quake a hero shooter! - but when the game went into EA and it was not nearly as bad as many had feared, many were convinced that it was worth giving them the opportunity to make the game good. Unfortunately, the developers of QC consistently squandered that opportunity. QC has been plagued with technical issues that have been solved in previous iterations of the series and, considering the nature of Quake gameplay, are entirely unacceptable, especially so long after Bethesda started charging money for the game. QC's technical issues are so bad that this year's QuakeCon tournament featured two complete game crashes.
The developers have also made numerous design missteps that also could have been avoided had they simply done things as they'd been done in previous iterations. Among the most notorious of these is QC's attempt to push a new duel format that emphasizes the "champions" part of Quake Champions. Duel has been the keystone of competitive Quake for a very long time now; one would expect that any alteration to the formula would not be done with a heavy hand. Nonetheless, what we got was a format that was almost universally reviled for its capacity to suck the air out of the room and for its ability to shine the spotlight on QC's greatest shortcomings. Consequently, one of the most consistent requests by the community is the return of the "timed duel" format that Quake duels had used for the preceding two decades. The developers eventually acquiesced, but the implementation of timed duel has been excruciatingly slow; indeed, ranked time duel is still unavailable and the uncertainty in changeover has rendered ranked play almost pointless.
There is definitely more to be said on the topic of how bungled Quake has been managed. Certainly there is a lot to be said about how inappropriate of a product Quake 4 is, for example, but I really wanted to focus on the way that Quake's handlers have even managed to prevent the good recent entries in the series from succeeding.
