Languages large swaths of the industry know (Java, C#, JS, Python, etc) include a subset of people who learned it purely for the job opportunities but aren't competent developers. The number of people who learn more niche languages like an ML or Haskell has a far lower % of people of that type.
An example of a language that I could see shifting from one to the other pretty soon is Rust now that it could be a way in to many of the high paying big companies like Google, Amazon, etc.