They haven't done it because they don't have many patents. It's easy to act noble about how you'll use your patents when you don't have any. Other commenters have noted that Google is currently suing Apple and others over standards essential patents (no just because the lawsuit started before their acquisition closed doesn't mean anything, they could settle or withdraw their case). Google had the opportunity to join a consortium with Microsoft to bid on the Novell patents, they declined. They could have joined this consortium as well but they decided to bid for it alone. Not only would it have shared the costs among the group, but it would have also prevented each other from suing over them. Google clearly wanted to control these patents themselves so that they could extract licensing deals from others, something that isn't so easy to do when you just have a license for a patent.