> In the 80s the idea of a library of functionality was something you paid for, and painstakingly included parts of into your size constrained environment (fit it on a floppy). You probably picked apart that library and pulled the bits you needed, integrating them into your builds to be as small as possible.

If anything, the 1980s is when the idea of fully reusable, separately-developed software components first became practical, with Objective-C and the like. In fact it's a significant success story of Rust that this sort of pervasive software componentry has now been widely adopted as part of a systems programming language.