If an exchange isn’t regulated by the government, then technically it can be considered an illegal operation.
Sure, there are DEXs around now, but are they really popular? Not really.
As much as some don’t want to admit it, we can’t deny that regulation gives users confidence. When an exchange is licensed and monitored by the government, people feel safer using it. Of course, the trade-off is that once an exchange is regulated, KYC becomes a basic requirement.
They are not popular, but they would be an option once the other side becomes unbearable to stay on, if such a time comes

CEXes are just more convenient and go a long way to stay like that..
It will never reach a point where it becomes unbearable, because the government will always make sure people stick to centralized exchanges. If traders start moving heavy into DEX and it gets too popular, the government will just go after the operators, and no one wants to risk their money under that kind of pressure.
Worse, it might even be treated the same way as mixers, and that’s the last thing we don't want to see.