Learn Russian: Почему он всегда сам носит чемодан? - Why does he always carry the suitcase himself?

Носит is the multidirectional verb for carrying by hand. Because of the word всегда (always), we are talking about a repeated, habitual action rather than a single trip in one direction. Therefore, we use носит instead of the unidirectional несёт.

The English translation says 'himself'. Why use сам instead of себя?

In English, 'himself' does two different jobs. It can be reflexive (as in 'he sees himself'), which translates to себя. It can also be emphatic, meaning 'on his own' or 'without help' (as in 'he carries it himself'), which is сам. Since he is doing the work independently, сам is correct here.

Чемодан is the object being carried. Why doesn't its ending change?

The word чемодан is in the accusative case because it is the direct object of the verb. However, because it is a masculine inanimate noun (an object, not a living person or animal), its accusative form looks exactly identical to its nominative dictionary form.

The current lesson is about the prefix от-. Why isn't the verb относит used here?