Why don't cats go to the bathroom??

My cat never goes into the bathroom unless I'm here.

And he almost never go into my bedroom when I'm sleep. He only goes there when I'm awake and doing other things. Sometimes he will sleep in my bedroom but only when I'm not here, and only on my chair never my bed.

He also almost never sit on the living room couch or my computer chair. He mostly prefers to sleep on the floor on a rug.