Isn’t it the lack of space/economics that is making them less tolerant of keeping junk around? Or do you mean something else?
There was some concern about liability. One of the shops I frequented in the late 1990's would only let customers who they trusted browse through their sorted junk piles. These piles contained things like bicycles, which had to be thoroughly inspected and properly repaired in order to be safe.
I also noticed a transition towards boutique style stores around that time. While the older stores may sell a box of books or bag of clothes for a few dollars, the newer stores would only sell items at their sticker price (or with a fixed discount during sales). Less product moved since people would only buy something when they felt it was worth the sticker price, rather than paying what they felt something was worth. The transition made space/economics more of a factor than it used to be.
Some of the old style stores still exist, but they are increasingly difficult to find.
I suspect that thet haven’t gotten any less tolerant, just what people are willing to buy from them at a cost that covers justifies the inventory space given competition for the space has changed.