In my experience, both as a musician and patron, if at the start of the tour, photos/video are fine, and then suddenly aren't, it means some shitheads started selling either photos or videos of the concert for profit without approval of the band. it ends up being a huge copyright pain in the ass when that happens. (you see it too with bands that allow folks to record audio of a show. if you walk into a record store and they're selling bootlegs for $30, you can bet that band will stop allowing taping pretty quickly).
either that, or the legal issues went sideways, but that'd be a stretch.
lord knows it's not because they sound bad (i've known a couple bands who got in the habit of phoning in shows who stopped allowing photos/audio/video because it ended up on youtube of them sucking balls and it hurt ticket sales) or because they're playing unreleased material (when i saw the frames last nov., they played a very new, very raw song and asked that folks not record it, and amazingly, everyone put down their phones), which tend to be causes of changing media policy.
this is all speculation of course. they might just have decided they were sick of playing concerts to iphones instead of people.