In my case it was the fact that fish's scripting language is incompatible with bash's that made me switch back to zsh (after a few years of using fish). It's not a show stopper (otherwise I had switched back earlier), but there's been a dose of small daily frictions because of that.

I try not to use nonstandard software unless it's something I spend a lot of time on. The shell became very important to my work recently, and only then I started looking for alternatives to bash and zsh.