> Why Elixir + Erlang are not more popular for high concurrency projects is a mystery to me.

1) Because the amount of "high concurrency" you can handle with a single machine with "standard" languages keeps moving up every year.

2) Because you had a single, nigh undocumented, very impenetrable to port implementation of BEAM for the longest time.

3) Because "Erlang" isn't the magic. OTP is the magic. And that requires that you shift your mindset dramatically. And you can do the OTP abstractions in other languages!

4) I think Scala sucked up a lot of Erlang's oxygen for a long time. Erlang is helping with that.