Answer: One will make lots of money for the tribe and the other doesn't belong to them.
The Skywalk is an eyesore in one of Earth's most beautiful places. Snow from the sky and man-made snow look the same.
Natives don't hold that every inch of Nature is equally sacred. The San Francisco Peaks are a specific sacred site.
Some tribes may hold the Grand Canyon sacred, but it's more likely to be the bottom (where they supposedly emerged from) than the rim. And if the Hualapai don't consider the rim sacred, that's their right.
Of course, the Hualapai tribe seems to be split on the Skywalk. Which would indicate that some Hualapai consider the canyon rim sacred and some don't. Indians that disagree with each other: what a concept.