Which kind of idiot says that to an elementary student? That incredibly dumb.

A teacher that actually needs to run a classroom.

When you have 30 kids in your class and 50 minutes to teach a 90 minute lesson, you have to do triage. There simply isn't time to litigate every single excuse a student may have for being late. Some will be the kid's responsibility, some not. Teachers don't have the time to call up parents and hold a detailed conversation or to investigate every excuse.

Instead, you just mark the kid absent or tardy. Then make sure the penalties for absences or tardies are light enough that a few won't hurt them. If they get to the point of actually having disciplinary consequences for their tardies, at that point you can start having discussions with parents to see if something the parents are doing is causing the kids to be late.