I suspect the people doing these things don't sit down ahead of time and think "Hm, if I get caught I could go to jail for four years instead of two... I'd accept two, but four is too much." Generally speaking the exact severity of the punishment isn't really all that relevant. It's how likely the person is to be caught at all that gives criminals pause.
I think the best thing to do would be to highly publicize situations like this where attempts to frame people fail. Make people who were thinking of doing something like this aware that they can be caught, and they'll hopefully rethink themselves. And ideally it'll be useful for the victims too, to be able to point to these cases when they tell people they didn't really say those horrible things.