Because then Google would be profiting from alleged stolen intellectual property and would be vulnerable to lawsuits.

Make no mistake - Google's ultimate goal with Android is NOT to make the best quality OS - but rather make it just good & attractive enough that the end user is willing to use it - and give it away to get it on as many devices as possible. Why? So they can push their ads out to it and collect data from the end user to tailor those ads. That is what is Google's cash cow.

Phone manufacturers have been put in a bind - they were all caught off guard by the iPhone. They had to scramble to come up with devices to compete with it to remain viable in this new, massive market. Palm attempted to blaze their own trail and create their own OS and ecosystem, but their device was junk (plastic screen?) and despite a rather nice OS, they flopped. It takes a lot of R&D to create a good OS and Apple patented many aspects of the touch UI. Other companies decided to get in bed with Google rather than create their own ecosystems and run the risk of facing a fate similar to Palm. Now they are facing lawsuits from Apple & Oracle, among others. The fact that Moto is exploring other options now is proof that perhaps sleeping with a partner that has to give away her goods might not be so wise in the long run.  ;)