I'm assuming they don't have legal requirements since they owned the old code anyway.
It could just be that they started using other proprietary components in their code though.
Would've loved to read the source code for Doom 2016!
I always found amusing that to replace him Zenimax built a whole new studio in Germany to hire the top programmers from Crytek and even then Doom 2016 used a litany of middleware :-P.
It was like the game didn't know if it wanted to be an FPS or some seamless open world ARPG so it tried to do a bit of both and the only reason the FPS side didn't felt bad was because id was masters at making FPSs by that time - but it was certainly dragged down.
It would have been way better if it was a regular FPS with a linear progression of levels like id's previous games.
https://www.gamedeveloper.com/design/patent-issue-forces-new...
With the newer engines there isn't a convenient branch that already has the proprietary parts substituted, and there's a lot more of them.
-----------------------------------------
John Carmack's .plan for Dec 11, 1997
-----------------------------------------
The Quake 2 public code release is up at:
ftp://ftp.idsoftware.com/idstuff/quake2/source/q2source_12_11.zip
This source code distribution is only for hard-core people that are
going to spend a lot of time pouring over it. This is NOT a
how-to-make-levels-for-q2 type dsitribution!
This should keep a bunch of you busy for a while. :)
https://github.com/ESWAT/john-carmack-plan-archive/blob/mast...