the question is, does the % of sales match the number of offered items.
There is no question that the volume of buying has not kept pace with the number of listings. But the level of buying is growing; so that means that "all the buyers" have not gone. They have just changed.
And most of it is the same merchandise.
That is also true for vintage sellers. My favorite music artist has about 6,000 items when I search. The vast majority of them are the same items from the same sellers that were here two years ago. One record I regularly search for has only I copy on eBay - it is a $5 record with writing on the label that has been listed by the same seller continuously for 5 years.
Search is one of the top 3 reasons buyers are leaving.
IMHO the top reason peopel are leaving is because the marketpalce has fundamentally changed, especially for "vintage" and "used" and "collectible" (however you define those).
In the early days, eBay was like the California gold rush. It started with a trickle and grew to a torrent as eBay "prospectors" staked out their claims, rummaging through attics, basements, thrift stores, and garage sales looking for something they could flip.
But now, 20 years later, there are no more wagon trains bringing new prospectors. The attics and pawn shops are mostly depleted, with only the occasional nugget turning up. Every record store owner I know - and I know quite a few - sells his best stuff on eBay, not to prospectors digging in the bins. They just get the tailings.
eBay is now ubiquitous, and has infiltrated every collector niche out there. There is no frontier left, so the only ones getting the steady gold these days are just doing math calculations based on surveys.
IMHO "search" is not the primary issue, and it pales when compared to the fundamental change in the landscape.
