In case you’re mystified why cats tend to sleep so much, you might also be mystified why water is wet or that fire is hot. It’s just a blatantly obvious fact of nature that cats sleep far more often than the Vice President of the United States.
The reasons are many. First, cats are predators so they need to rest to conserve their energy in case they need to wake up and hunt something down. Second, cats just tend to sleep often because that’s what they do. If you feel your cat is sleeping too much, chances are good you have too much time on your hands to worry about your cat.