The reason why Google bought Motorola Mobility for 12 billion dollars and sold it for three is that it stripped the company of most of its patents before selling it. Patents are what enable companies to use technologies without having to pay expensive licensing agreements with patent owners. And failing to do so can result in extremely costly legal battles.
Lenovo has its own share of patents, and there are a few little stringy bits of IP flesh left on Motorola’s bones. But without the old library of Motorola patents to hand, making a new phone as cheap and good as the Moto G may simply not be possible.