Mixers were used to have more security to their holdings as well as for the purpose of anonymity. People using it a way to stay secure on the illegal business. For this we can't go check every address from which the transaction has taken place.
Some users have suggested for a block of specific address within exchanges, but that isn't a possible solution and that affect the circulation in the market. Rather than making large funds idle let it get circulated.
Mixer services are expensive and quality of mixing service you use is unknown. If you are not a technical guy and can not check their quality (if you know to that, you would have not use their mixing service), you simply believe in what they advertise and use their service. By that I meant, your anonymity can or can not be protected by the service you are using for your bitcoin transactions.
Use non-custodial wallets
Turn on Coin control feature
Use change addresses
Use Tor when you broadcast your transactions
Use Wasabi wallet if you need to use Coin Join.
Most "tumblers", like the now-defunct bestmixer.io or even ChipMixer, aren't great because they are needlessly expensive, you're trusting the service not to run away with your coins, and you're trusting the service not to keep logs. Maybe they're the best current solution for small amounts where lasting anonymity isn't mission-critical, but in most cases you shouldn't use them.
Anonymity is very difficult, especially with blockchain-based systems where so much data has to be public, but also in other areas (eg. there are several known weaknesses with Tor). You should always operate with the expectation that any anonymity system you use will eventually fail you. If you're ever confident in your anonymity, then you're wrong.
