One word. Law.
As Florian Mueller has pointed out, many times now, Google faces an immense potential liability from Oracle's copyright-and-patent suit. The suit isn't against Android per-se. It's against Dalvik, the Java Virtual Machine (JVM) written to run Java-based applications. The Google legal team did not do their homework before letting this semi-proprietary thing into the wild, and Oracle may justify its purchase of Sun with one law suit as a result.
While Google and Oracle are both part of the Open Invention Network, the patent consortium designed to protect Linux, the suit is about Java, not Linux. The OIN has not, and will not, interfere, even though OIN head Keith Bergelt has made noise about wanting to protect Android in the press.