Why do students skip class?

= Because they are not interested in that subject.

Why are they not interested in that subject?

= Because that subject is not interesting at all.

Why is the subject not interesting for the students?

= Because the students think that it's an useless subject.

Why do some of the teachers need to teach that useless subject?

= Because only those teachers are good in that subject.

Why the teachers like that subject but the students hate that subject?

= Because the teachers fail to make the subject interesting, they make the subject more boring instead.