Lots of people were saying that YouTube could be monetized, especially by Google, because Google needed content, which YouTube had, Google wanted to get into the booming video landscape and Google had massive bandwidth, which YouTube desperately needed. The only issue was how fast Google would clean up all of the copyright infringement and how it would affect YouTube.
It turns out what Google was buying was a chance to maintain their lead in how people were going to use their computers.
Facebook is now buying a chance to maintain their lead with how people are going to use their phones.