AFAIK before the commit Doom was under a more restrictive license [1]
" For educational purposes only, you, the
end-user, may use portions of the Source Code, such as particular
routines, to develop your own software, but may not duplicate the
Source Code, except as noted in paragraph"
[...]
" Under no circumstances shall you, the
end-user, be permitted, allowed or authorized to commercially exploit
the Software. Neither you nor anyone at your direction shall do any
of the following acts with regard to the Software, or any portion
thereof:
Rent;
Sell;
Lease;
Offer on a pay-per-play basis;
Distribute for money or any other consideration; or
In any other manner and through any medium whatsoever
commercially exploit or use for any commercial purpose."
" For educational purposes only, you, the end-user, may use portions of the Source Code, such as particular routines, to develop your own software, but may not duplicate the Source Code, except as noted in paragraph" [...]
" Under no circumstances shall you, the end-user, be permitted, allowed or authorized to commercially exploit the Software. Neither you nor anyone at your direction shall do any of the following acts with regard to the Software, or any portion thereof:
commercially exploit or use for any commercial purpose."[1] https://github.com/id-Software/DOOM/commit/4eb368a960647c8cc...