init scripts were so simple they could be understood just by looking at the name: the computer is Initialized by Scripts. Systemd was much more complex and allowed many more tools to interact with the different parts of the computer, but people had to learn these tools. Previously all a person had to understand to deal with the computer was how to edit a text file and what various commands and programs did.

It's complex because it solves a complex problem. before people had to hack that together with complex init scripts, now they can let systemd do the hard work.

A comment from an Arch Linux' init script maintainer: https://www.reddit.com/r/archlinux/comments/4lzxs3/comment/d3rhxlc/