If I Fit, I Sit
The capacity of cats to "comfortably" squeeze into small areas never fails to astound or amuse us. Instead, cats may relax in any number of cozy spots, such as the cat bed you bought them. So why do they pick places like boxes, bathroom basins, little baskets, etc. to curl up?
Your cat feels comfortable and secure in small areas. They wouldn't want to be unguarded in an open space if they were living in the wild since doing so would make them more vulnerable to predators. Cats naturally have the urge to ambush prey. They can keep an eye on and examine their environment from a distance by hiding in tiny, cramped places.