Tell me then, if Purgatory is such a vital and necessary part of our transition into Heaven, why pray for those undergoing it? Why ask for their comfort, their expedited processing, their release from it? Why tell people that prayers to Mary - who is claimed to be the Queen over Purgatory - gain her merciful acts to free the souls still there? If, as you say, this place is only a necessary, final step to glory, why should there be anything said, done or paid to hurry the process up? Why rush perfecting?
Because we do not stop to love our neighbor after they are dead.