Okay, so some clarification: Bitcoin mining doesn't have anything to do with GPUs or GPU availability/shortages. It's entirely ASIC and has been for almost a decade.
It's Ethereum mining that's the GPU blackhole. There are other cryptocurrencies that you can mine with a GPU, but all of them together is only a fraction of ETH's network. Some of these are pegged against BTC, so their value increases and decreases with BTC, but for the most part ETH holds its own value.
And that is going to go away in the next few months when ETH 2.0 is implemented (which no longer depends on GPU mining). We'll have a period when there's no profitable GPU mining and everyone would be scrambling to dispose of their ill-timed investments, but that will not be for long. This window will be the best time to get a hold of a GPU. But it's inevitable something else would come in and take ETH's place.