Don't see why his humour would not stand up today, and if it didn't it can change. Read a biography of Morecombe and Wise to see how they changed over the years, they did not start off as a pair of idiots. Or look at Frankie Howard, went out of fashion but came back big three times.
It's quite possible he is comfortably off and doesn't feel the desperate need to be top of the bill, they way some stars do. Plenty of stars take their foot off the accelerator after 5 years of headlines and go into semi-retirement doing things they enjoy instead of a constant round of provincial theatres, bland hotel rooms and 1,000 miles a week travelling.