Because I'm worth it!
Google is today where Microsoft was a few years ago. Made and unmade at will. Innovated, created trend, if not give them head companies bought or copied directly nullify competition giving away free what others charged ... In buying businesses, it would be the first and last that caught and kept it in the closet and never heard.
For Google, I suppose, does the same, you see something interesting in Motorola, know-how, patents, whatever, buy it and then sell it.
Lenovo looks the same at Motorola, a company that was a leader and benchmark (there were many years was synonymous with Motorola mobile phones) have something to offer. Therefore, these are comings and goings of interest, you probably will not be able to imagine, or perhaps as simple as the premise of the whole company, which is, "make money."