So, Mixers provide service of shuffling bitcoins or provide addresses loaded with bitcoins along with private keys. In short, they provide service so to create anonymity between sender's and receiver's address so that no one can trace the transaction.
My question is why not use Exchanges? When we deposit funds on exchange, bitcoins get deposited on exchange's cold wallet. But when we withdraw funds, withdraw gets processed from exchange's hot wallet. So in short, it is very easy to do anonymous transfer by depositing funds on exchange and withdrawing to other addresses. Why to pay 1-3% fees on Mixers when it could be done for much less on Exchanges. Exchanges like Binance charge just 0.0005 BTC to process withdrawals.
Mixers guarantees anonimity of the trader's address both the reciever and sender by breaking the links of both addresses making them essentially untraceable. Meanwhile, exchange requires log data, so if unfortunately the exchange got hacked and entered by hacker obviously your data will be put at an abvious risk including your bitcoin and the transactions that was supposed to be private. So why use mixers instead of exchange? It is simply because of the guaranteed anonimity of my identity, transactions, and address.