There is: "This place is standardized on X" (what is way more common than it should be.)

And: "X-developers are cheaper" (and then, developers stay stuck there because it's a large market, but shouldn't.)

And there's the real reason why one should want to use the same language everywhere, that is to provide greater integration between frontend and backend on a framework (but then, currently it's mostly React that tries to do that and it doesn't get good results out of it - so much that developers refuse to use that feature).