The truth is, he hasn't written (or at least presented) that much new material in his standup act in the decades after he finished the TV show. And that's OK, as a millionaire, I'd probably achieve far less than he has since the show (it's not not just standup he's been doing). But in an article praising his productive habbits, this strikes as a bit ironic.
In HBO's Talking Funny [1] (from 2011) there's a discussion (around 1:00–2:00), where it's pretty clear how his habbit of replacing old material in the act is far more infrequent and little-by-little compared to the other comedians around the table, who generally throw away their entire hour almost every year after a special.