Because - and there is no denying how epic Groudon is - a lot of people (myself included) run straight for Groudon. Completely bypassing the fact that Primal K is a beast. Rain teams can be hellascary to go up against and I still have not seen any ways to counter/OHKO Primal K. Sure there is Cradilly. But I don't fancy taking an "ice beam" to the face. Get my drift?
Well, your more then welcome to have some VGC matches with me if you like?