I use fish because I have better things to do than tweak my shell configuration and debug shell plugins.
When I tried oh-my-zsh and prezto (I think?) they came with tons of plugins that performed badly and made it hard to get things done (specifically, they ran git status synchronously on every new prompt, which does not work well in a moderately large repo). Fish had similar features but wasn’t horribly slow, so I use it.
Lovely! Where I’m from, we call those horse apples.