Google To Launch Venture Fund
techcrunch.com
techcrunch.com
As other people have pointed out, they might have. I imagine the reason it isn't successful is the same reason government sponsorship of startups isn't successful - bureaucracies tend to not work very well when it comes to having to often admit mistakes and changing course - sunk costs bias and all that.
You must not be aware of who works at Google... Peter Norvig and Guido van Rossum come to mind. Granted, in the domain of advising startups, Paul is both a lot more knowledgeable and accessible.