Why should some speakers need a big room?

An obvious response is that some speakers might not fit in the space.

For instance, imagine a pair of Sound-Lab ultimates in a room 10 wide, 12 long with 8 foot ceilings.

The speaker is 38 inches wide, and allowing only 8 inches from the side walls (which is not enough), the distance between them would be only 28 inches.

With spikes, the speaker would be within inches of the ceiling too. Not great for sound or looks, regardless of volume played.