The design changeover is being driven from the top. Ever since Steve Jobs has died and Larry took over as CEO, he's gotten the design religion, and his goal is for Google's design to remain fresh and drive trends forward perpetually. So as far as the company is concerned, this is a feature, not a bug. It's true that the individual designers responsible for doing the design often vary from project to project. However, there's a fair amount of continuity as well. The designer who initiated the design refresh announced today has been with the company since 2006; the designer I worked with for the visual refresh of 2010 now heads up design for all of Search. They are explicitly told by executives to make things fresh and remove previous constraints when imagining the new Google.
No wonder Android gets redesigned very year, management wants it to be "fresh". Problem is that design should be driven by function, not by a desire to be hip. I think that's why Android designs always seem shallow and poorly thought through below the surface.