I doubt most instructors would deliberately demonstrate a bounce, simply to protect the aircraft. It wouldn't surprise me if most of them will take over if they see that about to occur, for the same reason. The result is that when it does happen to a student when they're flying solo, they're in an unfamiliar situation with very little time available for a decision, when they're already fully engaged in trying to do a landing.
I was lucky enough to have instructors who let me make that mistake multiple times, so I got plenty of practice bouncing down the runway - and learnt both of the standard recovery techniques.
The situation is similar to the light twin engine failure on takeoff training. It's really important that students have that experience so they can respond instantly - but if the student gets it wrong and the instructor isn't ready to step in immediately then the consequences can be catastrophic.