> A PhD is a program to compete for academic prestige

That's true for some people but others have different motivations, such as learning useful skills so they can gain the ability to work on interesting problems in a given field.

Doing a PhD in PL can also help you get the kind of jobs you mentioned, and achieve more once you're there. For me, the most valuable I thing I got out of the process was extensive exposure to the literature, which has been useful in a range of contexts.