The problem is that Erlang and its BEAM-based descendants still seem to be the only languages that actually do get concurrency completely right. Lots of languages have some form of an actor model, sure (whether as libraries or - like Pony - baked into the language), but all of them seem to rely either on OS threads per process (which are obscenely heavy) or green threads / coroutines (which lack preemption) (if you happen to know of any other languages/runtimes that offer lightweight preemptive concurrent actors/processes, let me know).

Until that happens, BEAM is unfortunately a hard dependency on getting the concurrency model fully "right".