They do it cause it works. When you've got a couple billion in media capital that you can fling around, it is very easy to just say "You're the pedo! You're the crook! You're the dictator! You're doing genocide!" on the loudest volume.

And it doesn't help when your opposition takes it at face value and announces "We're looking into whether we're all degenerate freaks. We're taking these allegations very seriously" in between sucking up to the same batch of billionaire sociopaths bankrolling the fascist movement.