Chapel and the other two languages were part of the HPCS project. An HPCS goal [was] to create a multi petaflop systems [1]. Erlang is not really the kind of language you can use to build such systems. It's not that Chapel (or the other two) 'obsolete' Erlang, it's that they were built with completely different goals in mind.

[1] https://en.wikipedia.org/wiki/High_Productivity_Computing_Sy...