Purely speculation on my part, but that makes a lot of sense. During the Ballmer era, he would have wanted to send a clear and unambiguous signal that he was no longer calling the shots, so he would have made a greater effort to step away. Also important was that, while Ballmer wasn’t technically a cofounder, he had been around since the early days. With Ballmer gone and Gates having demonstrated that his foundation is by far his #1 focus, there’s less reason for him to give Microsoft some distance and more reason for him to occasionally show up and, among other things, serve as a living connection to their early history.