i think because a multi players can play with one kinect while if you want to play a 4 player game with move then you should buy 4 move for example you want to buy the move bundle for 100$ + 3 move sticks for 3 X 50$ = 150$ + the optional analog controller for each move 3 X 30$ = 90$ and now count .. 100 + 150 + 90 = 340 $ !!??
move cost 50$ for the motion controller but
you also need the optional controller for some games which is 30$ more
so if you want the compete set for one move then you should pay 70$ + of course the ps camera.