This is a pattern with every such environment I can think of. Most people are unlikely to stop at a random house on a street with a sign out front saying "Stuff

This is a pattern with every such environment I can think of. Most people are unlikely to stop at a random house on a street with a sign out front saying "Stuff for sale," and will instead meet that same seller with that same stuff at a flea market, because the flea market provides some small aura of respectability. But not a ton, so even more people will only shop at a "real store." The marginal cost of selling out of your house is essentially zero, but your market size is tiny. The flea market costs a little bit, but gives you a little bigger potential market. Getting into a retail store or a big online store like Amazon costs even more, but gives your a much bigger potential market. So as a seller, you do it, but of course all such outlets eventually try to maximize their own profits at the expense of the sellers, and so it continues.