If the school did not taught you that, why would the job do?

Because sooner or later everyone realizes that - with the exception of people aiming for education grants or university eduction - school is an artificial, self-contained environment and things that happen there have little consequence. When you stop caring whether you get C or E on anything, the school loses its power to teach you punctuality and reliability.

Punctuality does not really make difference between C and E.

In my experience, people who were not at time in school, were not at time in their jobs. And either they found a job where it did not matter or were in constant trouble because of it or got fired.

Generally, they did not acquired puntuality nor precision. The lack of either was result of general attitude toward everything around and it did not magically changed after school.

Well, normally the forcing function for school, if school itself doesn't work, is parents.

But if your family sucks... School won't save you :-(

Indeed. And unfortunately, quite a lot of families are dysfunctional, for various complicated reasons. When parents offload parenting to schools, while schools expect kids to be parented at home... kids parent themselves.

Cause school does incentive some people because there no short term benefits especially if you make Cs and just dont have the skills to become a white collar worker. This goes especially for disagreeable young people.