For lots of reasons. Some folks are superstitious (some don't even realize they are). At some point in history cats were thought to be the devil and were killed, so the rodent population booms (and brought on the Black Plague, tra-la). Some people just don't like animals that get underfoot, which cats will do when they want your attention. There's the control thing--cats can be independent and have a mind of their own and many people want their pets to fawn at them, do their bidding, respond to commands as dogs do. Cats in general are not pack animals so feel no need to do tricks or bring your slippers or whatever. Cats also can get along without humans, which some people find totally unacceptable. My mom used to hate cats because the only ones she ever knew were half wild, brought home fleas, were usually kind of dirty from being outside all the time, would come home torn up (and most died since no one ever considered a cat was worth the price of vet care) and/or pregnant, would shed on everything, would bring inside the house live mice/birds/bugs/etc., and would jump on the food-prep surfaces. But once she met my cats, she's reconsidered and was surprised that cats could be so soft and clean all the time, well mannered (mine don't get on the counters and eating tables), respond and are demonstrably affectionate to me, come when called--plus their catbox never reeks (another thing mom never liked). My dad hates dogs. And I love them all.