I think section 230 immunity shielding from from any liability is also very motivating. Google was born into a world where companies had 10,000s of support personnel, today there are companies with over a million employees, they could easily human-review every single ad and they probably would if they weren't able to divert that cost into profits without consequence. AI makes it even easier and cheaper but... why bother?

Then there's the profits from scams, Meta is the only one with the stones to admit they like scam ads because they make up 10% of their revenue. I doubt it's a massive coincidence all the other big platforms are overrun with scams they do as little as possible to police.