^that's because theirs are basically serrated steak knives. Amazing for tearing off chunks of flesh but not so much for robustness. (Compare eg. the massive peg-like teeth of crocodilians, optimised to survive holding on to large struggling prey.) So the things come off altogether relatively easily rather than break partially and leave inconvenient gaps and have whole rows of backups constantly growing behind.
...yeah you don't actually want to get playfully or inquisitively nibbled by those - that's in fact what most shark attacks on people amount to.