For a period in the Ballmer era it was said that Gates had entirely disconnected to focus 100% on the charity work. There is some surprise that Gates seems to be more involved in the Nadella era given how strict Gates was said to be hands-off during Ballmer's tenure, though certainly it is still no surprise that the charity work is still Gates' focus.
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.
That doesn't really make a lot of since though. Why all of a sudden for the younger one? He spend most of those years in command for Microsoft, before focusing on charity work from 2008 and up. (His children would have been roughly 12, 9, and 6 at that time.) So, that may be a part of it but probably not a major part.
Ah, I was under the impression that he had stepped down in 2008. But that was probably from any activity at Microsoft and 2000 was when he relinquished the CEO title. Thank you for clarifying that. It does sound like that may be more closely related than I thought.