The ones who use the mixers already know that they can do what OP shared with us in this thread but still they prefer to use mixers. The mixers have some extra perks and they can reduce someone's precious time and the reliable ones never run with your money.

The exchanges especially decentralized exchanges can't be trusted because they can be rug-pull schemes. I have seen many decentralized exchanges that scammed their users and took a rug-pull type of exit. That's another reason to not trust the decentralized exchanges.

The game is totally different with centralized exchanges as they are already connected with the governmental organizations and as soon as they receive a suspicious transaction, they will freeze the accounts that receive such transactions.

If your coins are clean then you may not need to fear anyways but if you bought coins from someone whom you don't know then you can still face some problems if those coins come from a suspected address. The mixers solve issues for such innocent people who buy coins from unknown people and may otherwise get strong actions against them just for the purchase.

I believe that's another reason which is stopping people to invest in Bitcoin because the big investors might fear that if the coins that they have bought somehow come from a tagged address then they might face legal issues in future. That's why they prefer to use mixers to be safe from such legal issues.