Why do they need another social network? If it helps youtube users, ofc its a good move. But if its means to an end, to create a social network -- I thought the

Why do they need another social network? If it helps youtube users, ofc its a good move. But if its means to an end, to create a social network -- I thought their main motive for having a social net of some kind was to use vote/comment/share signals as additional data to improve search and ad placement, given that those are more informative than which link of the ones offered by search you choose to click. But they don't need a massive social net just for that, and they have G+. Isn't that enough to do the job?