Maybe there is such a non-compete clause, and Bill just doesn’t care anymore. “He will NOT be ignored!”.
Larry King went through the same process. He refused to accept that his time in the sun had come to a close.
Bob Barker resisted retiring for years and years, well past his 80th (!!) birthday, or at least it looked that way.
What BabyBoomer among us could forget how the great comic Jerry Lewis was unceremoniously DUMPED from his MS Telethon.
Sometimes, there is no going back, at least not to the same level of prominence. Billy-O may be the exception to the rule.
It shows you how smart Jerry Seinfeld was. Go out on top.