Because the apology is so shallow and glib and self-serving that it's literally worse than no apology.

It might be a bad and insufficient apology, but people always say that, about all apologies, even honest and good ones. A more workable policy would be to never criticize apologies, but accept them and move on. You never want to make apologizing a sure-losing move.

Yes, but the apology should not affect the likelihood of being punished. If you do something bad, apologizing shouldn't be a ticket out of punishment.