They could. But they don't.
I've seen this up close. The regulatory bodies as a rule are understaffed, overworked and underpaid. I'm sure they'd love to do a much better job but the reality is that there are just too many ways to give them busywork allowing the real crap to go unnoticed until it is (much) too late.
Because they’re put there as a box ticking exercise without ever being given the power or resources to be able to do damage or negatively impact the bottom line of the big rule breakers. It’s just supposed to maintain the appearance of doing something without ever supporting these activities for real. For the most part they are a true Potemkin village. If the risk is diffuse (just some average Joe suckers will lose money) I wouldn’t hold my breath that anyone is controlling for real.