What do bunnies mainly sleep on in a cage?

If you do not have a wire bottom cage I wouldn't worry about it. My rabbits are always switching where they want to sleep. One day you will find them all laying on the bottom of their cage with all of their blankets and beds on the other side of the cage. Then other days you will find them on or under their blankets or on their beds. But their favorite place to sleep is cardboard boxes.

Being a very vulnerable prey species, it's natural for a rabbit to burrow in the provided bedding. As to why it won't use the hide provided is a little more obscure. Like any individual your rabbit probably just has a preference. If this concerns you, you may try placing a variety of hide spots for your rabbit. The eccentric plastic hiding places are abundant, but I find that a dome that is light-tight to be more readily used. Depends on the bedding you use, you may want to overload the huts with bedding, in order to allow the rabbit to burrow in their hide-out.

If he doesn't use it-- no big whoop.

Take care.

They actually dig up the bedding and make a bit of a nest around them they don't mind sleeping on the wire bottom with their bedding around them for warmth.