That's a perfectly relevant thing, no?

Yes. The entire reason I like using Java at my day job is that the rest of the company uses it the most and supports it well. I would never use Java on my own, but they made it work ok here.

It reads as a little bit of a tautology. "People are using it because people use it". I get that from a hireability standpoint it's a real thing to consider, but the statement doesn't say anything about whether or not Python is actually a good language to use

Another counterpoint to this. Rust is a popular language (debatable claim, of course) but it's not high in corporate demand.