To the Holy Souls in Purgatory, the people still living on this earth are like millionaires. The people living on the earth have access to the spiritual treasures of the Church and to the merits of Our Lord’s Passion. If they are in a state of grace, they can freely avail themselves of those treasures.
The living can (and should) choose to bestow these spiritual treasures upon The Poor Souls in Purgatory, just as a wealthy man can and should give some of his wealth to the poor. A millionaire can easily help the poor. We can easily help the Poor Souls in Purgatory. If this is not done, when it can be done, an account of this neglect will have to be given to God at our judgement.
Think about it: how much time and effort does it take to say prayers for the Holy Souls in Purgatory each day. The answer is: very little time and effort.