Saw this article the other day explaining FB decision to purchase WhatsApp as well.
http://www.businessinsider.com/why-face ... app-2014-2
I think the reason they are going on this purchasing rampage is to protect themselves. They literally can't
afford to have even the slightest amount of competition.
Part of the reason they allow users to upload an unlimited number of photos and videos for free is to keep you coming back. Lets say a new a new photo sharing company opens up "RealmMinePics .com" and allows you to upload photos. Even if "RealmMinePics .com" is better at sharing photos in every sense, you will still have all of your family vacation photos on FB already. Its inconvenient for you to re-upload everything again and get everyone of your friends to go there.
There are many other reasons of course as to why FB is going crazy doing this. Personally Im kinda hoping FB dies out after time. "Social" media sometimes makes me feel like we are being waaaaayy antisocial when i'm sitting at breakfast and my roommates are all facebooking instead of talking lol, but thats probably more a cultural/generational thing.