I'm not sure why they are the most common type of anthropomorphic characters. I know that Japanese culture reveres the wolf and fox as Shinto spirits traditionally. They do have and like dogs, but are more likely to own cats. The 'maneki neko' story associates cats with luck. So you see a lot of wolf, fox, and cat anthros in Japanese media. There are a lot more dogs in American media (such as Disney movies) because Americans like dogs so much. It's probably just a cultural preference for certain animals. Could also be geographic, you need a lot of space for dogs, cats are better suited to small, urban apartments - like most people have in Japan. There are less anthro farm animals because I think so few people live outside of cities as much now compared to like 100 years ago, in either the U.S. or Japan. They had anthro sheep in 'Catherine', a Japanese anime-style video game, because of a joke on the association of counting sheep = sleep. These were terrifying. I'd like a show about more of a variety of anthro animals that are cute. We got Squid Girl? Lol. Cats, cats, cats, with the occasional wolf or fox.