I'm a bit confused because you compare that experience to modern programming as a software developer. I think you are thinking of the difference across 40+ years, rather than the difference of kid vs. adult.
I mean, if you were programming on a Unix machine in 1983, or a VMS machine, or an IBM mainframe, you would have far more than a single manual.
The point I was trying to make was about the distinction between programming with a limited set of building blocks vs programming with a large and open-ended selection of libraries. They don't require the same skill set, and one seems more fun to me than the other.
Mechanical engineering is a lot harder, there are so many options to consider, new options come along all the time so you're always falling behind, and cost plays a much larger and - I think - more boring role in the process.
I think that is analogous to the point you are making with computers.