Why did Facebook buy Instagram?

Hey guys, Jordan here back with another post, this post is about the big news that Facebook has bought Instagram, I mean thats ok, but the thing I can't believe is the price, $1,000,000,000 <--- :O.That is just soo weird, but yeah so Facebook, nice one! So, the first thing I want to talk about is the people who use Instagram, for those of you who don't know what Instagram is, It's a photo sharing network for Android & iOS and you can share your photos on Facebook & Twitter.But, the thing I don't understand is why Twitter didn't buy this first, I mean about 90% of Instagram users post to Twitter, not Facebook.I prefer to upload photos to the actual Facebook, not from Instagram.But, there are tons of Ways to post pictures on Twitter, Twitpic, The official way, yet most people use Instagram.I thought Facebook were just going to make it for Facebook, but I don't why Mark Zuckerburg bought Instagram for that price & yet is allowing them to put up their photos on Twitter aswell, because I don't know anyone who uploads via Facebook.So, yeah what do you guys think? I think it was a waste -Jordan