In my experience, this is usually the result of DRM. Most of my physical library of PC games doen’t work because they use some kind of variation of StarForce. If you go back far enough, yes the old 16-bit titles don’t work, and DOS hasn’t been properly supported since pre-XP. Things like games not supporting widescreen resolutions or running some kind of bizarre deprecated library is often quite fixable. For all the criticisms I have of Windows, getting old games to work hasn’t really been one of them.

Games for Windows Live can go to hell though.

Yeah, because at least a decent 3rd party might hand you documentation and have the sense to build something consistent or maintainable. AI has a limited context scope and frequently suffers a type of short term memory loss that results in repeated work or variations in work that confuse the end result.