These executives, though, also made billions in investments themselves in Microsoft's Redmond Campus, which mostly otherwise will stand empty.

These executives don't like looking dumb and these billions in useless investment are statues to them looking stupid otherwise.

Those investments would be a matter of public record, either directly or through real estate companies. Any investigator who found these hypothetical investments would get a lot if clicks and eyeballs so there is a hell of a lot of incentive. So where's the proof?