I think you underestimate how many different vintage platforms there are out there. There was a HUGE diversity of computing platforms in the 70s and 80s.
Just looking at one list: Apple II, Apple Macintosh, Atari, Commodore 64, DEC Rainbow, IBM PC, Kaypro II, NEC APC, NEC PC, Osborne, TI-99/4A, TI-Professional, TRS-80, TRS-80 Model III.
And within many families you have different, often incompatible models. Some games will run on only certain specific models within those families. For example a "TRS-80" game can be specific to the original TRS-80, Model II, Model III, Model 4, color computer, etc. Others programs may even require specific configurations of sound cards, graphic cards, and input devices for the best operation. For example, some "PC" games have the best sound only on a Tandy 1000. Others require a 386+, while others are incompatible with anything later than a PC XT
The combinations needed to run ALL games in ALL the universe is almost endless.
And that is not even getting in to dedicated game consoles!