Isn't Instagram still using AWS for some of their infrastructure? They had a big blog post about moving but if i remember correctly there was article about instagram getting hacked via S3 bucket keys a couple months back.
I always suspected that Facebook's purchasing of Parse was an aquihire. (I've used Parse from 2012-2013)
This seems like Facebook throwing in the towel on what seemed like a good plan to gain a foothold in the cloud space.
Either that, or they're not really shutting down, and they just want to get a bunch of free labor from open source developers before migrating to an enterprise support business model.