That's true, but if they are in an enclosure, obviously they can't get out. As they feel around the tank a few times this is practically realized, so if they are in a bigger tank, they don't feel as safe, since there is likely to be more open space instead of things to hide in. In the wild they normally find burrows in the ground and termite mounds to hide in, but are normally pretty well hidden. I wondered about this myself for a while, but it really comes down to the awkward realization that BP's love to be in a "snug" environment. Helps them feel safer.