It's not that WordPress, the technology, is simple. It's that deploying the bog standard solution, rather than investing energy into researching alternatives and developing workflows for them, is a simple and pragmatic approach.
Those sharp edges aren't really relevant anyway on a hosted service (wordpress.com) where they are buffed out for you.
I don't like WordPress either, I prefer static site generators, but if you're going for something simple and fast to setup it's a legitimate choice.