I don't hate PHP, but I am wary of developers who only work in it. For the same reason I'm wary of Java developers, though.

A language is a tool and should be treated as such. Trying to force every problem into a single box is skin to the "everything is a nail" idea.

That said, I'm not sure Rust was the right call for the Lemmy backend, either. I like Rust. My team is transitioning to it for a system level service. But we would have chosen a different language if our goal was a web backend.

The thing with open source projects, though, is often times they are written in the language the developer is learning or working in at the time, not because the language is the most suited for the job.