deposits land instantly but withdrawals take days — why

Genuine question that's annoyed me for years: they can take my deposit in half a second, but sending my own money back takes days. How does that work then?

Officially it's security checks and payment processing. Unofficially, some sites sit on withdrawals hoping you'll reverse them and play it back. The good ones approve quickly and the money moves; the bad ones use pending as a business model.

Also worth knowing some genuinely do batch-process payments at set times, so a Friday night withdrawal can just be unlucky timing. Still, the instant-deposit-slow-withdrawal asymmetry is mostly a choice.

pending as a business model

That's the phrase I've been looking for for about five years. Spot on.