When you installed an app, it usually just went in a folder. Sometimes it was just one file. There wasn't a mass of dependencies and complex systems to manage them. Just some libraries built into the system.
Modern macOS is a bit like that too, except it has all the unix under there too, so there's a mess of files all over the place. There are many files hidden from the user (which the user wouldn't understand anyway). Whereas classic macOS had a beautiful simplicity where you clicked on the system folder and there was Finder and other things which were at least somewhat understandable to me as a kid.
I had Strata 3D, which I got with an educational discount. That was the software used to make Myst. Our Quadra 700 only had 8mb of RAM and I was trying to render a spaceship flying through mountains on a distant planet. I managed to replace the Finder with Strata (using RezEdit) and boot into Strata. The machine would crash if I clicked on the apple menu, but this got me a bit more RAM.
Anyway, something like NixOS addresses the flaws of Unix package management, but it requires quite some complex machinery to do so. AFAIK, we didn't have the versionitis issues on classic macOS, but again, I was just a kid. It was a simpler time.