On the contrary, it is an act of charity to pray for the holy souls in purgatory. It is true that they will eventually get to heaven, but our prayers can help them get there sooner and they can do nothing to help themselves (unlike those still living, who can help themselves). And, although the holy souls cannot pray for themselves, they can pray for us, particularly for their benefactors. Given their utter vulnerability and dependence on the charity of others, it is reasonable to assume that God might be particularly attentive to the intercession of the holy souls for the needs of their benefactors.
