Why is it that what is beneficial cannot always be called good?

Because we are not doing good for ourselves, we will definitely not get any benefit from this. It is possible to give good only free of charge. But bad deeds are most often more selfish in nature, in other words, the benefit in this case is present. We try to achieve a certain goal when we do something bad. Good can rarely be beneficial, and usually such a benefit is not intended. In bad deeds, on the contrary, it is the main goal; without it, no people would not have done anything contradictory.