I feel like there has got to be a better common denominator if you're willing to stick with just Linux.
Yesterday I was trying to track down why a bash script that worked on pretty much every platform I'd tried and across a bunch of different bash versions was not working on a new operating system. Turns out the script was relying on "non-standard" behavior in tr(1). Definitely not the first thing you think of when you see bash complaining about undefined variables.
A bit further back I had similar fun with FreeBSD's installer now that they've ripped perl5 out of the base system. The installer is, of course, an unholy mix of C and sh.
Well, there is Perl, which is what actually was used to be for "can we do this in something that is not shell but also portable?" kinds of scripts for quite some time. But then again, it's Perl.
Why is this a thing still? Who is out there saying "We want you to develop an app but we won't let you use Python"?
Granted, I really wish there was a python-lts that didn't break stdlib stuff every few years, but it seems like everything remotely modern breaks compatibility constantly...
Not many people are saying that, but there's a few cases it could make sense. Like if you want to setup something on an embedded machine with no/restricted internet, then bash scripts will be easier.
Some people also like not having to do extra installs to run something simple.
And some scripts are simple enough that it's just easier to use bash.
But I agree, these cases are pretty obscure and most of the time the benefits of using a real language is worth the investment.
I can see it being useful in certain situations, but I would think most use cases would benefit most from a better language.