Cats on average sleep 16-18 hours a day depending on age. Cats in this time often appear to be asleep but this varies from their deep sleep, that is why they can be awakened easily. A lot of the time they are in a light sleep, sleeping in shore increments of 10-30minutes at a time.
So in this way they don’t sleep as much as you think. Because cats use a special sort of sugar to fuel their short burst of activity, they are very careful when and why they rush into action. Whether a domestic, outdoor or indoor cat they still instinctively want to hunt so are always conserving energy for that. In the wild it would be vital to their survival as they may not have enough energy to catch the vital prey that keeps them alive.
Footnote: Cats are most active at dawn and dusk. You wondered your cat constantly wakes you up the early hours of the morning? Now you now, it is natural to your cat. They are not being annoying it is how their body clock works, SO DON”T BE TOO HARSH ON THEM!