okayyyyyyyyyy so this is what we're told what happens but its not the case. unsold donated clothing rarely gets given to impoverished countries. actually what happens is pretty shitty.
ok so basically donated clothing gets sorted into 3 main categories: able to re-sell (what you find in thrift stores), clothing that is too soiled/damaged often gets shredded and made into other products like furniture stuffing and insulation. but then there's another category of clothing that falls in between those two categories and we're told it's just given to poor people but it's not.
what happens is that clothing gets packed into crates and shipped off to 3rd world countries where it's NOT divided among the unfortunate, but buyers bid on it for re-sale in their respective countries. which doesn't sound so bad except 1. its an incredibly risky business: a good crate can yield good money especially if it contains multiples of the same items (often used as work uniforms). but if the crate doesn't have much, that person can become completely broke over it. its an industry that really doesn't benefit anyone. 2. like i said prior, one of the best industries to help developing countries climb out of poverty is the apparel industry (yep, it's a fucked situation where kids working in a factory also means that family finally has food on the table). But they can't DO that if there's a steady stream of donated runoff going into their country. basically, clothing donation "charities" make money by helping to keep developing countries down.
Even countries that make their own clothing just re-sell donated clothes because it just easier and has a higher profit margin.
if you want to get rid of your clothing, try to give it to people directly first: people you know, local shelters, etc. If you want to donate it try to find a thrift store that has a well-curated stock: you'll get a decent amount of money and it keeps that clothing's longevity and away from the abovementioned shit industry. but ultimately people just got to be buying way fucking less.
info about used clothing auctions is getting harder to come across but here are a few good articles about donating clothes: