How do you know it? Today you have to re-assess what you've learnt in the past. If you think JVM is "simply more employable" and haven't tested the waters in last 1-2 years, chances are you're just wrong.
The feeling I have: more simpler the tech is (and JVM/Ruby/other CRUD), the highest salary cuts you're getting. And you're actually less employable.
It is that counter-intuitive, because it's one person with a coding agent vs a team in the past.