I think, but I cannot supprt it with evidence, that the reduction in supply is caused by a number of factors: 1. Strong hands. People are buying for their sets, focusing on higher end material and just not willing to let it loose. 2. Pandemic-induced increase in buying, particularly on the web. People who otherwise would not have ventured onto the web for their acquisitions were forced to by the pandemic, wound up liking it, and then did more of it, further depleting supply. When they could go to the rare show, they took advantage and bought more than they might have pre-pandemic. 3. Strong equity markets making people feel more comfortable spending money indulging their hobby. Not to mention some "free" government money. 4. The pandemic induced a shift in spending from services to goods. Coins are goods and our market saw a relative decrease in material in the face of increased demand. That's why prices are rising. It isn't that there is a dramatic decrease in material, it's that there is a big increase in demand making it appear like there is a big decrease in supply. I'm not saying there isn't a decrease in supply, just that what decrease exists is appearing larger than the reality.
Lots of sales have moved to the internet. Even the big auction houses are doing extremely well. With most of the shows closed over the last year or two, there has not been as much coming back in. Prices are strong for most pieces and going up. With many people stuck at home, a lot more browsing and buying was going on. I still much prefer to see a coin in person to get a better feel of the strike and luster, hard things to capture in pictures.
That's what everyone needs, an automatic cat. Covid is probably a big part of it. For the past two years a lot of people haven't been going to shows because either the shows were cancelled or people were worried about getting Covid (This is to a large extent a hobby of "old white guys" and many of us are in the high risk category) But they have still been BUYING online and from dealer websites or auctions. This means a LOT of material going out, but without the in person meeting between collectors and dealers, not a lot coming back out into the dealers hands.