[danmaz74]

Speaking for myself, it is because I see google as something that brings you traffic (and revenue if you use adsense), not as something that tries to bring away your traffic: You go to google to leave it as soon as you find your destination, while you go to facebook to stay there... and facebook is trying to cajole everyone into closing themselves inside their walls, with their pages, their apps, and so on.

Of course, with Google betting so much on G+, this could change. But I can still hope that google will try to differentiate itself from FB, at least in the eyes of developers, by being more outwardly than facebook. If they can make an offer that is more compelling for third parties, not driving them to completely relocate themselves inside the G+ environment, they could benefit from that in the long term.