It could stop it if all the players would act as they should, but a lot cheat.
To cash out from an exchange you don't need just the selfie, you also need a bank account with that name, you need to get the money out of that bank account if al the banks would really employ KYC and AML policies this would become harder and harder and what's more important, far costlier for a thief to do so.
But yeah, when there are people acting knowingly as mules, selling the usage of their bank account knowingly for pennies, things get a bit messy.
Also, there are other ways of cashing out, not directly via a bank account.
You know that event from your own country, and I have a feeling the same is happening in mine with an ATM network, not giving names but since it's one of the few which posts online the sums available in their machines it's pretty easy to guess. I've seen some pretty weird numbers on their machines, sometimes there are days when they lose only 5-10k euros from their available balance and then in a matter of hours all the machines around a whole area of the country are down a few hundred thousand euros, and more, their balance goes down to 50-100 euros, so somebody that is almost counting to the last euro.
I just wanted to say that mixers just semi-anonymize the source of the funds, if people want to point them as the ones helping scammers cash out they are overlooking other and more important links in the chain