The trouble is that most of the other services can be improved by access to the social graph. And since Facebook isn't likely to share the social graph with Google, Google have to build their own. The driving force for the change was a company wide belief that Facebook would eventually make Google, by offering competing services that was superior because they had access to the social graph.

Source: http://www.wired.com/epicenter/2011/06/inside-google-plus-so...

That is also why Google+ is everywhere (and why it was named Google+). It is Google plus the added value you can get from social graph. The +You part of the service itself is not the main point, even though it of course provides some potential ad space.

Yes, there are potential anti-trust issues. They can be seen as somewhat analogous to Microsoft bundling IE with Windows. That gave Microsoft a lot of trouble at the time, but today few would question that a consumer OS should include a web browser. Bill Gates saw where personal computing were headed, and reacted rationally.

Maybe search (and friends) can stay competitive without access to the social graph. I don't know. But Google don't believe so.