Presumably because MSFT is the most highly diversified tech company on the planet and he's overseeing multiple billion dollar businesses there without breaking a sweat.
Not to mention the only big tech that seems to have a coherent AI strategy at the moment.
To be fair, MSFT was the most diversified tech company prior to his arrival - Google had Search, Facebook had Facebook, Apple had hardware. Microsoft by then had perhaps a dozen products with a billion dollars or more of revenue (Windows, Office, Sharepoint, Exchange, XBox, Azure, Surface, among others). Satya did well to focus on the cloud and grow opportunities there, but he hasn't significantly increased the diversity of the product lineup.
If you look at the charts with revenue streams - Microsoft is the most diversified in that regard, because basically each and every branch of Microsoft produces the similar amount of revenue.
With Xbox getting Activision it lifts up More Personal Computing to the level, comparable to other streams (and even higher than Windows).
Not to mention the only big tech that seems to have a coherent AI strategy at the moment.