Because taking money from a con artist to deliver marks based on profiles you've collected on everyone to see who's most likely to be taken in makes you an accessory if not accomplice to fraud.

Businesses (in particular the literal biggest ad agency in the world) should know who they are partnering with. Not vetting the people they're allowing to place ads is at best negligent. The fact that the FBI warns people to use ad blockers to protect themselves from fraud (instead of anyone doing anything about it) is shameful. Someone either approved the scams or the system which allows these unvetted partners to operate. There should be a criminal investigation into how this came to be. Especially considering people have anecdotally said online that they've reported scam ads and received a reply that the ad was reviewed and determined to not violate policy (that may be Facebook, or both. In any case this applies to anyone). At that point they unambiguously have actual knowledge of and are a participant in the fraud. People at these ad companies should be looking at prison time if that is indeed happening.