Two considerations:
Large speakers are usually designed that way to accommodate larger woofers. This may overdrive a smaller room. Also, remember that nearly all speaker cabinets vibrate to some degree, thus they add to the soundfield. The larger the cabinet, the more potential for this.
Second, larger speakers may have drivers spaced further apart and require a more distant listening position to allow them to integrate. Also, in producing more bass, they may need placement further away from the front and side walls, thus requiring a larger room.
Large speakers are usually designed that way to accommodate larger woofers. This may overdrive a smaller room. Also, remember that nearly all speaker cabinets vibrate to some degree, thus they add to the soundfield. The larger the cabinet, the more potential for this.
Second, larger speakers may have drivers spaced further apart and require a more distant listening position to allow them to integrate. Also, in producing more bass, they may need placement further away from the front and side walls, thus requiring a larger room.