Simplicity is definitely something to be valued, but for some reason Linux people equate "just a few shell scripts" with simplicity.

Sure there might not be much there, and maybe if you read all of those scripts you can understand them. But I don't want to have to read and manually maintain the shell scripts of my init system. That isn't simple for normal users. Simple is when the OS actually works reliably, and shell scripts are the antithesis of reliability.