There may be many reasons why a cat may see its owner sleeping. Cats are free animals, so they may just want to see what their owners are doing. Cats may also find their owner's bed comfortable and want to sleep next to them. In addition, cats may be protecting their owners - sometimes they will "guard" their owners to prevent other animals or threats.
However, sometimes cats may see their owners sleeping because they themselves want to sleep - cats sleep 16-20 times a day Hours. So, if your cat often comes to sleep with you when they see you sleeping, it's probably because they're looking for a comfy place to sleep.
