One of my theories is that there isn't actually enough honest companies buying ad space to satisfy the shareholders in companies like Alphabet or Meta. If they actually care to also filter out the ads for junk products and services, there would probably be a minor collapse in the industry.
Honest companies are priced out by scammy companies, and as long as these companies share the profits they are totally fine profiting off scams. They make more money off the scams, simply put.