There's a lot of chatter going on on a couple other forums, including some feedback from someone at B&H. The explanation given seems pretty thin; the only specific info I found was that they were restricting shipment on Class 9 hazmat, but I can't find a comprehensive document that explains that standard. Unless it's incredibly broad in defining "hazardous," I can't see it covering virtually all photographic chemicals. Stranger still, lithium-ion batteries, a documented hazard, still seem to be available for shipping.
It sounds to me like there's more to the story, but I don't think we'll be hearing it, nor do I expect the situation to be reversed.