It's probably due to his recent stroke, although Keillor had already shown he is a lousy satirist a few years ago. But what he's written most recently for the Chicago Tribune goes beyond inept satire.
My theory is that Keillor is too much the canonized Great Man of the Arts for any of the cultural gate-keepers to stop him - and one of these days he's going to say something so offensive even they won't be able to palm it off as "he's only satirizing" - they're going to let him drive his addle-brained self right off a cliff.