Erlang requires a fair amount of boilerplate for a small project (rebar, app file, application behaviour, gen_server behaviour, etc.) and escript doesn't work very well.

It lacks a good way to do abstract data types (records don't count).

The compiler's ability to optimize is limited by the lack of purely functional guarantees and the metaprogramming facilities (parse transforms) aren't easy to use to work around that.

There's no facility like Haskell's ST or clojure transients to encapsulate mutable stuff, just a hole to write code in C and who really wants to do that? Yes, I know about the process dictionary and ets but those aren't appropriate for most algorithms I've wanted mutability for.

That said, I still use Erlang, but only in the domains where it really shines.