Before bash was the world's default shell, it was csh, then tcsh. At my university, if you switched your shell to bash, the sysadmins would put you under extra scrutiny, suspecting you were a Linux user and thus likely to cause trouble.
We switched to a default shell with incompatible syntax not because of network effects but because it was much better than tcsh — initially just for scripting, later for interactive use as well.
zsh already existed at that point, btw.
As for mastering bash? Nobody masters bash. Brian Fox hasn't mastered bash.