Why are gatherings always on federal land?

Even if the gathering is in a state with legal recreational weed, if it's on federal land then possession of marijuana is still illegal. We get cops driving through constantly to the tune of "Six up!" and some people get busted or have their pot confiscated. So why have it on federal land compared to state or private land?

 

Private land use definitely out. Nobody wants to take responsibility. You could lose your land!

 

How could you lose your land if you had the proper permits?

 

Nobody will give permits to the Rainbows.
You don't need a permit on private land unless it affects the local community.

 

Still, why could you lose your land if you host a Rainbow Gathering?