The two outgoing execs explained this as a "natural time" to streamline management now that Alphabet is "well-established" and its various brands (including Google) are operating smoothly as independent companies. Alphabet and Google just don't need two CEOs and a President, Page and Brin said. They pointed to Pichai as a logical pick given both his extensive experience and his "confidence in the value of the Alphabet structure."
In other words, Pichai is unlikely to toss out the existing formula. Alphabet will continue to rely heavily on search, cloud services, Android and Chrome, all the while branching out with more adventurous efforts like Loon and Waymo.
With that said, the management shake-up comes at a rough time. Google employees have accused their employer of cracking down on worker organization, taking a lax attitude toward sexual harassment and otherwise being unresponsive to staff concerns. It's also grappling with weighty issues like political ad integrity and accusations of bias. These problems aren't going away now that Pichai has more power -- he'll just carry a heavier workload.