A) It’s a National Park and you wouldn’t be able to have a city esp with a Walmart on a National Park.

B) Like 90% of Arizona is untouched wilderness and undeveloped. Why would you want to develop at the bottom of the GC when you could develop literally anywhere else in the state? The cost of transporting construction materials, given that there aren’t any roads from the surface to the bottom, not to mention logistics for people living and working in the Canyon, would be astronomical.