Why does Petco charge such high prices for their products?

Specifically, I'd like to know why a 30-pound box of Arm and Hammer Super Scoop cat litter costs $18.99 at Petco, while Petsmart charges $11.99 for the same box and Target charges $11.49 for a 35-pound box. Petco charges a whopping $7 more!!

Cat litter isn't the only thing that costs more at Petco. When we first got our dog, we regularly bought some 100-percent chicken treats for her. They were about $6 or $7 more at Petco than anywhere else.