Several reasons, among which include our co-founder is a co-author of the FreeSWITCH book, we love FreeSWITCH's eventing model, we built Whistle in Erlang and Andrew Thompson (Vagabond) had already built mod_erlang_event so we can tap into the event system with native Erlang terms.

We believe strongly in open source wanted every piece of the puzzle to be open source.