I recall a articale I read "somewhere" that reported the Facebook makes big profit (Billions) from scams. So they have no ( or no strong motive) motive to shut such scams down

An example is courtcase against Meta for using a Australians mining billionares likeness to promote a crypo investment scam.

https://www.afr.com/technology/dad-it-s-a-fraud-call-that-sp...

I'm surprised legitimate companies don't pressure Facebook on this though. There are enough scams on Facebook that I now refuse to believe anything there, even though some of the things look useful and probably are not scams (and also are things I didn't know existed without an ad - thus filling one of the legitimate values of advertisements: informing me of things that would make my life better but I don't know exist).

This is actually illegal here in Sweden though. Lawsuits are ongoing.

I'm kind of surprised that there haven't been criminal cases.

Your first assertion is obviously untrue. And fake celebrity endorsements pre-date the existence of the Internet, let alone Meta. There were lawsuits back in the 1800s on this topic. This is hardly a new problem unique to Meta.