Frankly speaking, because no-one is forcing them to stop serving them.

That's the biggest 'trick' companies like Google have pulled here. They've somehow tricked the regulators into thinking that because they're big companies serving a lot of customers over the internet, that any sort of fraud or product liability laws are irrelevant to them.

Because any other company doing this would get sued into oblivion, shut down and the executives criminally charged. If a brick and mortar business let blatant scammers and criminals advertise in their physical stores, that would be seen as a serious crime.

Same with a retailer that sold dangerous or counterfeit products, or one that turned their stores into surveillance panopticons where customer data was collected illegally and sold to the highest bidder.

Google, Amazon, Meta etc are doing things that would get a normal business owner sent to prison.

The solution isn't just technical, it's about being willing to enforce the law for internet businesses the same way we do for offline ones. If Sundar Pichai and the board were looking at 10-20 years in prison for fraud or cyber offences, then Google would fix those dodgy ads real quick...