A lot of UIs designed by developers without going through a real design phase end up only making sense if you already have a mental model that more or less matc

A lot of UIs designed by developers without going through a real design phase end up only making sense if you already have a mental model that more or less matches how the software works under the hood—the easiest UI to implement is usually one that doesn't provide any abstraction over the inner workings. So you end up with a steep learning curve, but software that is usable once you understand it. That's entirely different from a software feature whose design makes it literally impossible to use.