I think the goal might be to have more control on android devices to make more money. Although I don't really see why they can't do that with the linux kernel,

I think the goal might be to have more control on android devices to make more money. Although I don't really see why they can't do that with the linux kernel, maybe the linux kernel sort of prevents them from collecting more royalties. But I agree that making a new kernel from scratch is not really a very good idea, unless it brings big improvements, which I doubt.