i use zsh, but i often invoke bash just to make sure some behavior is "normal" rather than zsh-specific, or specific to how i wrote my .zshrc last decade [and haven't changed].

i don't think it's about the newfangledness; i think it's about the potential for subtle differences in syntax which scare people away from zsh.

I think the initial setup can be quite daunting; unlike bash, which never seemed to have moved beyond 1990, zsh added a lot of features, many of which are very useful (some of which less so, like csh-compatibility things) but there's a lot of it, and the defaults are somewhat bare-bones. Hence things like oh-my-zsh, which is quite intimidating in its own way.

The fish shell "fixed" a lot of that by adding more or less the same feature-set as zsh but without the extensive configurability, which is a really great trade-off if the fish defaults work well for you (they don't for me personally though).