Maybe he figures it's like going to a casino. When you've been winning like crazy, you have to realize your luck can't go on forever. Take your chips, cash them in and get out now. Or maybe he realizes it's just a matter of time before he won't have chumps like Obama and Kerry sitting across the table from him anymore, and the last thing he wants is to try to deal - speaking of casinos - with President Trump.
Whatever the motivation, Reuters reports that Ayatollah Khamenei issued an awfully weird directive on Tuesday: