Because (wisely) Microsoft is not going directly after Google, but after Google's users. Google is distributing the software for free, so in a court Microsoft would be hard pressed to show any illicit profit, or an added value for the patents it claims are infringed. Google would definitely fight back, the legal battle would last decades, and the patents would be exposed for all to be seen and worked around. Microsoft is playing the same game that Prenda Law played until recently, taxing the Android OS just enough that a manufacturer might prefer a licensing agreement to a fight in court, but at the same time adding a price tag to the the competing OS to make its own offer more competitive. I wouldn't be surprised if part of the settlement was a clause requiring the victims of this extortion scheme to produce a certain number of Windows phones, to try and convince the market that it is a relevant product. Recently they claimed 100 million copies of windows 8 sold, but how come they have nowhere as many activations? Because those copies are forcefully installed on machines that are then downgraded, or just sitting on shelves. The same goes for their windows phones: retailer bought them, but the consumers prefer other alternatives.