TrumpetMan
Android Enthusiast
I would speculate it's simply because with the huge back-order, by keeping it available to order online they'd be perpetually sold out and would never gain enough stock to ship to retail stores. I would imagine that after the stock has been replenished (last reports show that the screens are being produced again) and the brick & mortar stores get them, then you'll see it available to purchase online again.
Man, if Otterbox and other higher end case makers aren't working around the clock to make cases for this phone they are missing the boat big time.