Many of the comments in this thread refer to the sheer inertia of millions of LOC of bash script in the wild. This seems to be the main reason why Oil shell[1] aims to be "an upgrade path from bash to a better language and runtime".[2]
If you're a bash user and you want your scripts to run under Oil, I recommend testing it! If your script doesn't run, you'll probably get a better error message than bash gives you.
Or you might motivate a change the OSH language (a cleaned-up bash). It's easier to change now than later.
I wish them luck.
[1] https://www.oilshell.org/
[2] https://www.oilshell.org/why.html