With all these saints in heaven and stuff, how come they collectively haven't stopped all diseases or famines?

What "saints in heaven"? There are only 4 by name! Two were taken while they still lived; Enoch, and Isaiah. Two were resurrected; Moses, and Jesus! There are some others but we are not told how many or their names (resurrected with Christ). Other then these, all other persons, whether saint or sinner, are still in their graves awaiting the resurrection.