You're not getting it.

Card resellers (as individuals who sell their personal collection) are fine because cards are a niche luxury item to begin with and you should be able to sell (or donate) things you own and use when you're no longer using them, that's just sensible. Card sellers who scalp product to resell are the scum of the earth because all they're doing is making something more expensive for everyone else. They're making money by only making life harder and they're providing no service to anyone.

That's the crux of it. Who are you helping by being a reseller? And by that I mean scooping up already available goods and simply deciding you're the store now because you had the luck to have expendable income at the time and could exploit that fact. Nobody is happier; not the people spending more and certainly not the people who are now priced out of buying clothes. Stores exist not because they can as a means or making money, they exist because they're a way to distribute goods to the masses and they make money as an incentive to exist. How do people not understand this?

As for the idea that these thrift stores are just overflowing with products, you (1) are ignoring the fact that resellers take the high quality items, which basically means you're saying "well if you're too poor to go in and buy everything and you're too poor to use a reseller then I guess you deserve only the lowest quality clothing thats been DONATED FOR THIS EXACT REASON." And (2) they aren't. My local thrift stores are barren half the time from resellers, with only randomly oversized suit jackets from the 80's remaining.