Elixir was literally written by a Rails core team member as a response to issues he had in working on enterprise Rails apps. The Phoenix framework as well was

Elixir was literally written by a Rails core team member as a response to issues he had in working on enterprise Rails apps. The Phoenix framework as well was written by a long-time Rubyist, and the book they wrote together, Programming Phoenix, reads in places like a treatise on lessons learned from working with Rails. So Rubyists (I myself have been one since 2011) are drawn to it because it essentially has been billed as a successor to Rails when you need to be concerned with highly concurrent, fault-tolerant, TDD-driven web apps. Most companies who have embraced it are former Rails shops... most devs who use it are former Rails devs.