In a sense a non tribe member is not on the same playing field as growers on the various plantations / states which exist throughout the USA .
First, non members, could be subject to the arbitrary whims of the DEA, the Indians presumably are not, since it was the FEDS that "recognized" their alleged sovereignty. So, less FED intervention.
Also the Indian Tribes motive is profit, for themselves, so they aren't likely to impose the same levels of controlling bureaucracy on themselves that a "state approved" grower must endure. So, less State intervention.
Plus they're Indians and they like to smoke 'em Peace Pipe...Pale Face.