Why isn't it used? It's niche and betting on such a small community is risky for the majority of companies. Why use Elixir when you could hire 10 engineers to pump out javascript. That's the mentality of most.
Hiring for elixir was great, it self selected people who wrote code as their craft. You kind of have to be curious about code to even be aware of Elixir, know how to write elixir. These types of devs would pick it up really quickly because the language is just so damn ergonomic.
I'm using Elixir now, and I wake up so happy that I get paid to do this. I am really blessed.