Because they don't need to go to the bathroom. In many cases their energy comes from the cosmos or from other celestial sources.
They don't need to rely on food like we do. One example would be the Silver Surfer who keeps saying "My Energy Is Replenished By The Cosmos" whenever someone offers him health food.
If we too could arrange for our energy to be replenished by the cosmos, then our fashion designers would get about the task of designing what we would call "overwear!"
Underwear? Who said that?
:lol: :lol: :lol: