TOD:
In my experience with people, animal lovers are animal lovers and many pet owners have both cats and dogs, and other animals too, like rabbits or horses. Yes, there are some who proclaim to be "cat people" or "dog people", but they seem to be in the minority. I was always a cat person until I finally became a dog owner at the ripe old age of 45.
As for the preference, many people prefer cats because they're simply easier. They don't have to be walked and they're much easier to potty train. And even when dogs are trained, you have to have a pet door for them or let them out all the time. Litter boxes are much easier. Also, cats are much better at entertaining themselves. They don't chew up the furniture or your shoes out of boredom.
People prefer dogs because they're much more attentive and loyal to their owners, whereas they find cats to be too aloof. Dogs can follow commands, do tricks, and accompany you on hiking trips. Plus, their physicality with all the hundreds of breeds is so interesting. Whereas cats don't vary nearly as much in shape and size. I'm sure there are many other reasons for preferences one way or the other, but I've found these to be the main ones. When I got my first dog (a retired breeding toy poodle who was six years old), the breeder said that my dog will love me unconditionally while my cat will love me when it's convenient. Clearly, she was not a cat person.