I don't understand the negativity here.

He is a top expert on a security topic. Running Android platform security gives him an opportunity to have incredible positive impact for many people---which he did for a decade.

People weigh trade-offs.

At the beginning, he may have had high ambitions to deploy interesting, research-forward ideas to Android; at this point, he has accomplished a lot of that. Maybe now, he is considering other factors.

Guessing that people are only money-driven or have made some decision because of threshold personal wealth is awful, especially if you do not know them.

Almost all academics I know (I am one also) are driven by personal curiosity, intellectual ambitions, a need to identify and solve problems, and a strong desire for positive contribution. I know Rene and believe this to be true of him.