Even if the supply is comparable to prior generations, demand is undoubtedly much higher than typical. It's been more than four years since Pascal, Turing was barely worthy a successor, a large portion of the potential market is spending more time at home due to the pandemic, and due to the release coinciding with a new console generation, there are an unusually large number of graphically demanding games being released around the same time, which surely drives demand even further.
This also happens to be the first time in several generations that NVIDIA has lead a launch with one of their big-die parts. Maxwell, Pascal, and Turing all lauched with x104 parts, with the x102s to follow several months, sometimes almost a year, later. Having potent mainstream parts and AMD's competition already available in quantity when the big die parts hit surely alleviated some demand pressure.
Yeilds are always crappy on big-die parts, at least initially, which is one of the big reasons NVIDIA hasn't been releasing them first, and why AMD hasn't been making them at all (Fiji not withstanding).