I would also add internationalization. There were multi-language games back in the day, but the overhead of producing different versions for different markets was extremely high. Unicode has .. not quite trivialized this, but certainly made a lot of things possible that weren't.

Much respect to people who've manage to retrofit it: there are guerilla translated versions of some Japanese-only games.

> this is all before you take into account that modern graphics and audio is bitmap / PCM and running at resolutions literally orders of magnitude greater

Yes, people underestimate how much this contributes, especially to runtime memory usage.