Since when Carmack was not cooperative? From his begining the dude kept finger file, gave people ability to mod stuff, gave them tools, later open sourced the game runtime and the tools: Radiant, qmap, qlight and others are still used at LARGE by AAA game companies - Call Of Duty for example still uses large portions of that engine that Carmack wrote almost 20 years ago.
I'm still amazed at how engine like the Quake 3 engine were scalling as computer got better. Some engine just stop improving with time but that engine just kept taking as much juice as it could from the machines.