Why can't my mother-in-law's crystal ball pick crystals?

You must be mistaken. Mother-in-law's crystal ball is on the lower floor, but the crystal on it is just a mechanism to open the channel to the lower floor, that is, after you fly over and take off the crystal, you will find that the two floors in the original place have disappeared. Then you fly and jump, you get to the lower floor, and then you can pick up your mother-in-law's crystal ball.