Anyone can learn a language. The .Net framework and the related ecosystem is huge. I’ve done front end work maybe a decade ago, I still do backend JavaScript and I know the basics of web technologies. But anyone would be a fool to hire me if they wanted a front end developer.
Even if I knew Java that doesn’t mean I could just jump in and start doing Android development.
I've done it. OOP is OOP, there are only different flavors.
I wonder to what extent an OOP person would be able to do a Haskell job (or a similar functional language).