Meaning that every C64 was like very other C64, so you knew what you had to work with on the hardware side.

You could see this with consoles as well, as the games steadily improved as developers learned how to push that fixed hardware around (though the cartridge ones often allowed in-cart chips to assist).

I guess we have gotten so incredibly used to either being able upgrade piecemeal, or simply replace wholesale every few years, that having a steady set of hardware to explore and learn has become "foreign" in a way.

Compare and contrast the C64 and say the RPi. the former was more or less steady for 24 years, while the latter have been releasing beefier variants every 2 years or so.