It takes a lot longer to sign something than it does to get a photo. So what you're basically saying is "fewer fans should have the chance to meet Stan on the last/only opportunity they're ever going to get".
SM obviously had to make a choice, schedule-wise, between autographs and photographs. Given that (a) people had already forked out money for the photos and (b ) it was easier to get through several hundred of them rather than fifty or so autographs, they made absolutely the right choice about which to prioritise.