I really don't see that as being the case at all. Motion Controls are awesome for certain types of games, and Arms was an obvious choice for motion controls. If you don't like motion controls, which seems to be the case with the OP, then that would be the case, but thats purely down to personal opinion. I haven't played Arms so maybe the game is better with a standard controller, I dunno, but the only thing that made me ever consider getting it was the fact that it has motion controls. Besides, it sold really well for a new IP and a 3D fighting game.
I think this just comes down to someone who doesn't like motion controls thinks nobody likes motion controls so that must have hurt sales. The Wii made it very obvious that people like motion controls.