One way I convinced hubby on giving Mr. Whistles(who was the pig we had at the time) a larger cage was I told him to imagine himself locked in a closet for the rest of his life. He'd have to poop, pee and sleep in there. Once or twice a day someone would come by give him a pat, some food/spot clean. But that closet was his own space to move around in. He sat on the thought for a coupla days but soon realized this is what Mr. Whistles needed.
Had he not made his decision or said "No". I really would have locked him in the closet for an hour or so.