Why pray to Mary and the saints?

It is a good question, and the answer is not that you cannot speak one-on-one with God: of course you can, and that comes first. Praying to Mary or the saints does not replace that; it accompanies it. It is the same thing we do among ourselves: when something worries you, besides trying to resolve it, you ask people who love you to pray for you, to lend a hand. The saints and Mary are family who are already with God and remain on your side. Asking them to intercede takes nothing away from God; it brings it to him together with you. With Mary, moreover, there is something of a mother: turning to her is letting yourself be led by the hand toward her Son. It is not going around God; it is approaching him accompanied.