So, here's my conspiracy theory (though it doesn't involve super international spies with cats and what not):
1) Late June/early July: Nvidia orders TSMC (in Taiwan) to halt all manufacturing of GTX1070 and GTX1080 cards in late June-early July and to begin reconfiguration of assemble for the Titan X product
2) Early July: TSMC complies, all GTX1070 and GTX1080 production is halted and reconfiguration of the assemble lines for the Titan X begins
3) Early August: TSMC meets the initial quota for Titan X production and halts production, begins reconfiguring assemble lines to begin producing GTX1070 and GTX1080 cards again
4) Mid August: TSMC completes reconfiguration of assemble process and GTX1070 and GTX1080 cards begin to ship from Taiwan to worldwide retailers
5) Late August: GTX1070 and GTX1080 stock begin to slowly trickle in
6) Early to Mid September: GTX1070 and GTX1080 "in-stock" status becomes more frequent as consumer sales begin to fall as demand is met (finally)
So, based upon my best two cents from my half empty piggy bank, we have the Titan X to thank for the scarce supply of GTX1070 and GTX1080 cards (though the GTX1070 isn't in as much demand as the GTX1080)