At the operating system level I would say the different requirements are probably the more relevant reason than people not caring. Modern operating systems, even ones optimized for weaker hardware, include a lot of stuff that was either not invented or at least not common in consumer PCs in the 80s and early 90s:

wifi
several encryption standards, especially TLS
many other network-related features; we're talking about a time before HTTP and most other modern protocols were invented
support for multi-core CPUs or even multi-tasking at all
modern memory management (paging, virtual memory, swapping...)
USB
proper audio output instead of just a few predefined channels
much more complicated video output
drivers for all the most common hardware so you can just install it and go
...

And that's not even talking about people expecting a modern-looking desktop environment, web browser, file browser, image viewer, text editor and so on. The linux kernel is modular so if you compile your own, you can disable a lot of stuff that you don't need to save space and with something written specifically for those old machines, you can strip out even more stuff you don't need.

That being said, the thread title is very misleading. In the video he states the OS he uses works on the original Pentium processor which came out in 1993. Four years after Reagan went out of office.

[–] CanadaPlus 2 points 10 months ago

That's a good point. Supporting all hardware in particular is a pretty big ask. Maybe you could cleverly fit memory management into a small amount of code, but a pile of arbitrary standards can't really be meaningfully compressed.

In the video he states the OS he uses works on the original Pentium processor which came out in 1993. Four years after Reagan went out of office.

I was wondering. That didn't look like an 80's computer.