Honest question. I have only seen the "it's written in X, so therefore it must be re-written in something nicer even though it is working" thinking from incompetent people who were just trying to take ownership of something they didn't quite fully understand. Though I never have seen it in a appropriately functioning commercial setting; if management is competent, they'll immediately recognize the high costs with no concrete benefit and say no.
It's one thing to say "we have to re-write this because it uses Java applets, and Java applets are problematic because Oracle is dropping support for them, so our customers are going to be screwed soon if we don't do something." It's another thing to say "we have to re-write this because it's in Perl because Perl is something I don't like."