Doom source code was released on December 23rd, 1997 (1). That was while it was still relevant.
Again this has very little real connection to a commercial company in its prime releasing OSS and sacrificing massive income.
All you've shown me is a programmer who got wealthy releasing the closed source games via big name publishers, strategically making their own company, then later released the source code for a well-past-its-commerical-prime game at minimal personal risk, in an industry at the time where old games die. Even remastering old IP games wasn't a thing yet.
Meanwhile releasing his engine brought him and his team much personal reputation, showing his amazing programming techniques and talent which helped the industry... even though no one cared to use his old out-of-date open source engine (aka little commercial risk)... which yes was novel at the time and respectable.
What does this have to do with OpenAI exactly? Or top end talent spending their prime at a commercial software company?
And I despise the heavily policed OpenAI approach to models so I have no skin in the game to defend them.
Because Carmack kept developing new engines that were better. He also made it easy for people to build maps and add onto the game.
You can earn both money and followers by holding back key pieces but still sharing with the community.
Check out the book Masters of Doom.