Cats are more individualistic than humans. Did your cat invent the game of fetch and then invite YOU to play? One of ours did! I've lived with 9(?) cats in my life, and she's the only one that did that.
Blame their different fathers! Their genes alone seem deterministic. I've rescued three stray families, and in each litter there were obvious behavioral demarcations between the offspring of each father (which I never met or even saw).