What's very interesting with these large collections is the fact, well, that they are large collections.
A large amount of anything becomes extremely problematic to deal with.
You may have, (as I have had myself) a small number of parts with some value; not necessarily a large amount of cash, but something of value to someone who needs it and is willing to pay something for it. That's easy. Sell a part, two people happy.
Now, multiply that by 1000 or more...and make it all one big mostly uncategorized lot. Big problem. You have to store it all, in many cases move it all, and even after an auction, only the cherries get picked. There's a good amount of cash someone has made, but the bulk of the stuff remains. I have been through this with family estate sales. I've seen it with Sheila Heaney when her company
https://mbzparts.com/ in Oregon tried to make a go of buying a warehouse full of old MB parts in Oakland, CA. Had it been 1/10th the size, it may have been possible. But the whole lot? Was like a drug lord trying to deal with millions upon millions of dollars, all in $1 bills. Very problematic.
Those who want the parts, well they don't want ALL of them. Those selling want to sell everything, at the highest possible value, even if the parts are exceedingly obscure.
I once went to a warehouse in the USA full of many old Mercedes parts. Nothing on the scale of what MBZ was trying to buy, or that Sotheby's auction recently. But plenty of old obscure parts. One beautiful wood dashboard caught my eye, from some 1950s era MB sedan. Gorgeous. NOS. Large. For a RHD vehicle! Not exactly a fast mover anywhere.