That's fine, but there is the responsibility for the safety of the tourists who would, anywhere else in the Canyon, have regulated flights. Just because the reservation wants to make money, doesn't mean they can be exempt from sensible safety rules.
I suspect now that many tourists will stick to the more regulated areas for their tours.
Unless I am misunderstanding, in this instance, regulated means they restrict the number of flights and type of operations. It isn't necessarily an indication of more or less safe, just that the National park is more fussy to prevent the area being adversely affected by aircraft traffic.
I take it they probably license out the rights to fly in the area so this also has a bearing on cost to operators?