If they can be bribed once they can be bought twice. And it's a reminder to everyone that if you aren't getting the engagement your content deserves then it's a possibility that you are being deliberately sabotaged.
Shenanigans are common, but this specific kind is not very common.
How could anyone know that? No government cares to investigate this sort of thing, and those individuals who could become aware would mostly be subject to NDA.
Because it's not hard to figure out 'something' is going on, and, the level of 'bribery' in general for these kinds of things at above board corporations is rare.
"Not hard" for whom? The individual private porn producers? ITT you specifically disbelieve those exact people!
Only those who work in the right positions within Meta or one of these other horrible companies would have a good view into this, and they have no incentive to set things right.