If you're trying to purchase a Pascal or Polaris-based GPU, then you are probably well aware that patience is a required virtue. The problem is that, as a hardware website, we don't really know whether the issue is high demand or low supply. Both are manufactured on a new process node, which could mean that yield is a problem. On the other hand, it's been about four years since the last fabrication node, which means that chips got much smaller for the same performance.
Over time, manufacturing processes will mature, and yield will increase. But what about right now? AMD made a very small chip that produces ~GTX 970-level performance. NVIDIA is sticking with their typical, 3XXmm2 chip, which ended up producing higher than Titan X levels of performance.
It turns out that, according to online retailer, Overclockers UK, via Fudzilla, both the RX480 and GTX 1080 have sold over a thousand units at that location alone. That's quite a bit, especially when you consider that it only considers one (large) online retailer from Europe. It's difficult to say how much stock other stores (and regions) received compared to them, but it's still a thousand units in a day.
It's sounding like, for both vendors, pent-up demand might be the dominant factor.