Incorrigible literally means they cannot be helped, and the fact is there are kids for whom that is accurate. Giving them one on one instruction doesn't help, because they genuinely do not care. It does take up the time of teachers and burn them out, though, so they're less able to help the kids who are struggling but actually want help.

It's important to distinguish kids who just do not care at all from kids who are struggling, but it's also important to recognize that the former really do exist.