Cats, like people, are individuals with their own distinct personalities. It sounds as though you have found the "lap cat" that so many humans crave. There could be any number of reasons for this, but whatever the reason, your cat is continuing her kittenhood behavior with you. Kittens love to cuddle and sleep in clumps; they are used to the sound of multiple heartbeats. Your cat has carried this craving for closeness into adulthood and you are the beneficiary. Enjoy!