Quake 1 gets its first major co-op content update in 25 years
The biggest and most damning mistake ID Software ever did was to always start fresh.
There was a generation of players who started with Quake and just kept on playing it. Same for Quake 2 and Quake 3. This meant that the FPS player base became very segmentet in a genre which has a pretty heavy learningcurve.ID Software never went the Valve route with a Steam like application with engine updates and so on, in the end they always abandoned the player base that was built up. Modders kept the quake games alive but they couldn't fix the game engines.Back in the day Quake series was the big games, not Counterstrike.
ID Softwares lack of investment opened up the door for Valve.It was theirs to loose and they lost it.