Caporegime
Broadly it's just supply and demand. Supply is actually up (they shipped more GPUs than ever in 2021) but demand is also up, from normal consumers and miners.
So specifically it's how much we want GPUs given how bored we've been, and how much miners want(ed?) GPUs.
It was a managed shortage to DIY builders IMHO - companies just diverted more supply to miners,and laptop/desktop companies. Its why I noticed for several months it wasn't that hard to find a decently specced sub £1000 gaming desktop or laptop. Even some of the miners realised that and tried to mine on gaming laptops.
In 2020 we had a true shortage,but with so many people and companies having WFH infrastructure in place by 2021,and the world opening up,I have a feeling gamers might have somewhat not helped their own situation by paying beyond the odds.