For the purposes of this discussion [1], Erlang is just Go except you don't have mutexes as an option at all, so anything you want locked has to be in a separate Erlang process (analog of goroutine). So if all you want is a shared dictionary to be used as a cache or something, it has to have its own process/goroutine, you don't get an option of just locking access.

Since that's how it works in Erlang, it has a bit of syntax grease around it, but not enough to make it just right; you've still got to do things like handle communication errors because it could be on a different node in a cluster whereas in Go it's just a local shared resource.

I think the main problem is that as useful as actors are as a concept, they're not a great foundational abstraction, which is to say, the base that everything is built on and you can't go below. It works, but then it means you're paying the full actor price for everything. But you don't always want the full actor price for everything, and you don't need to pay it because in practice "lack of actor isolation" is rarely the root cause for any particular problem, because that's too big a thing to be the root cause.

[1]: If that's too glib for you: https://news.ycombinator.com/item?id=34564228