When buying from an exchange, you're essentially going on a list that says you bought Bitcoin and how much you own and at what price you bought it. On robosats or bisq, there is no "list" being made unless your peer is a fed. Your fiat payment rail (strike venmo zelle cash app PayPal etc) only knows that you sent fiat, they don't know what it was for. The whirlpool aspect is to then break the link from where you got it and from your future spends. So if you received sats in Bisq or robosats, your counterparty can follow your utxos to each future hop on chain. If the next hop is whirlpool then they cannot confidently follow it further than that first hop. (Robosats is lightning native so you can receive via lightning and avoid some of that traceability. Although many coordinators on robosats do allow on chain payouts which I prefer)