I think this is a misapprehension -- there is a ton of regulation around sports gambling. They may not have put the specific regulation that you think is necessary (in this case, banning advertising) but there are pretty huge barriers to entry to get into the sports bookmaking business, including a number of background checks and interviews in an attempt to prevent organized crime from getting a foothold. This is why every time you see an add for gambling there's a note on the ad saying "if you have a problem with gambling call this help line".