As an IC, I care about the market. I go to work exclusively to exchange my labor for money to support my addiction to food and shelter. When it was time to change jobs as your bog standard enterprise dev, it was much easier to throw my resume in the air and get a job offer by being an experienced C# developer than it would have been if I had spent three years writing software in Erlang.
And most job interviews outside of tech companies where most developers work are not going to be language agnostic nor are they going to have you reversing binary trees on the whiteboard while juggling bowling balls and riding a unicycle on a tightrope.
As a reformed former dev lead, why would I hire an Erlang developer when I could throw a rock and hit a good enough C#/Java JavaScript/React developer to push out some CRUD SaaS app or line of business app?