Not really, you're not seeing bash have many more features because its simpler on the inside at the cost of sometimes breaking. Rather, it seems an example of " the most dangerous enemy of a better solution is an existing codebase that is just good enough"

Not sure that is the real reason. Zsh was not free software in the Linux formative years. It lost its chance, and mindshare, like so much commercial Unix

Zsh was never part of a commercial Unix, so I suspect you are thinking of Ksh. As far as I can tell, Zsh has always been free software: the earliest version I could find used the GPL, but it now uses something more MIT-like.

Bash is probably more widely used because it was available earlier than Zsh, and because it was the "official" shell of the GNU project (better marketing).