Probably for the same reason my husband likes to nap on the floor rather than on a couch or bed. He just does. It sounds like she just likes sleeping under the bed. There's nothing wrong with that, and as you can see from the responses in this thread it's not unusual for a cat to like to sleep under the bed.Well maybe I shouldn't have said hiding, but I don't understand how she would rather sleep under the bed than on top of the comfy bed. I will put her on top of the bed and she will not sleep there. The first thing she does is goes under there. It's not like she's scared of any of us, but the only way she will sleep in our rooms is under the bed. Sometimes she will come out from under the bed over night to sleep on the bed or to get attention.
Sinbad';s favorite place to nap is beneath the "tent" that is formed when I sit on a chair, put one foot up on an ottoman, and drape a blanket over my lap. He curls up around the ankle that is on the floor and snoozes as happy as a clam.
My cats have always liked going underneath the bed - to sleep, to get away from loud people, when they don't feel well. Mingo actually gets inside the box springs to sleep. He hangs in there on the scrim, like it was a hammock. I think they like it because being under the bed is like being in a cave or a nest, and it's instinctive for cats in the wild to have a nest.
I've seen some cat beds that have a cover on top making it like a cave, and I'll bet a cat would like that, just like they love to get in boxes and paper bags.