Because then they won't get bribes later on. Money is like pretty or lucky. I've heard no one realistically so "You know, I have enough money. I have all the money I want. No thanks." and mean it.
But let's say it happened. They got caught, on film, giving a bribe. It'd be denounced as Deep State or Shadow Government if it's a Republican. If it's a Democrat then it's BURN THEM LIKE A WITCH!