Not only that, but the strength of bash is its ubiquity. (Or for that matter, posix sh, if you want even more ubiquity.) If we started adding lots of features to bash, it wouldn’t make sense to use them unless you are positive every place using your script has a new-enough version installed. Which defeats the purpose of the main use case for bash in the first place, which is (IMO) for portable scripts that will run on any Unix-like system.