Imagine you went through the pain of learning it to make a web front end. You want to make back end things too, but they all require knowing different languages. You’re not learning another language, learning this one was hard enough! Easier to keep using the same horrible language for everything, of course.

Relevant xkcd

Same principle as a former burglar who now installs security systems or a former soldier who now works as a bodyguard. You’ve got the skills, you just want to use them in a different way!