[easychris]

I think it's also about the ecosystem. With Elixir all third party packages etc. can be relied on having no side-effects / immutability.

If you try to code functional in an OOP language, you would have to make sure that no third party modules (or coworkers accidentally) write code that "misbehaves" in such aspects. Just like you currently have to make sure that the Ruby code you use is threadsafe.

With immutability you gain all those features baked into Erlang/OTP (scalability, reliability).