Coupons for a Cause

At Publix, when you donate $1, $3, or $5 to the Children's Miracle Network, they will give you a sheet of coupons totaling over $10. If you plan to buy the items with coupons anyway (which include items like Del Monte fruit cups, Uncle Ben's Ready Rice and others), you can donate to a good cause for what amounts to no cost to you. Why not?