Malkster, you are so correct. "It seems designed to prevent us from understanding it."
Once upon a time (I've been a Mac user since 1989), Windows users had to know DOS. They had to be almost programmers to keep their machines functioning. Mac users, on the other hand, were designers, musicians, and creators. They didn't know what went on under the hood and didn't care, but Macs functioned without tinkering anyway. In fact, as you say, Apple designed their machines to prevent the user from understanding them (you needed a special tool to open the case).
Twenty years ago, among other things, I was the Mac IT manager for a large company and was responsible for 140 iMacs. I was allocated two hours a week – and that's all I needed. The company also had 12 Windows machines and a full-time IT manager to keep them running.
Macs are supposed to run without fiddling, tweaking, or tinkering. Unfortunately, MacOS has become so complicated that many users are now expected to open Terminal and learn text commands like it's 1989.
Luckily for us, the machines will likely continue to run for years without the user ever learning terms like 'System Data'. The Mac will ultimately clean itself up and will only grind to a halt if it is genuinely stuffed full of photos and videos.