Cat biologically move in circular motions when using the litter box so why are most litter boxes rectangular?
Cats are biologically wired to turn and dig in circles when they eliminate. Less Litter's circular litter box lets them do exactly that, turning freely in any direction without hitting a wall. Rectangular boxes are only as wide as their shortest side, which means your cat is constantly working around a shape that wasn't designed for them.
A circular interior allows cats to fully utilize its unobstructed space they need to complete the circular motion comfortably whereas rectangular litter boxes are limited by their narrowest side, cutting your cat's movement short.