[reducesuffering]

Where did you read that? I believe Whatsapp used erlang because they leveraged ejabberd [0] for XMPP. Wouldn't surprise me if this is why FB originally used Erlang for the chat servers too. [0] https://en.wikipedia.org/wiki/Ejabberd

[darkr]

Yep. Facebook chat was originally based on ejabberd.

Source: https://web.archive.org/web/20121224094022/http://cufp.galoi...

[fineoldcannibal]

I believe it was because of the Beluga acquisition which was in Erlang