If you look at different dog breeds, you may notice the huge variation in size and shape. Even though they may be both dogs, a pitfall looks different from a dachshund, which looks different from a St. Bernard, which looks different from a poodle. Yet cat breeds mostly look the same size with minor visual differences.
The reason is that humans have been breeding dogs for several hundred years while people have only been breeding cats for approximately 75 years. Given enough time, perhaps cat breeds will start to look as weird and wild as dog breeds do.
Of course, breeding often creates unwanted side effects where certain breeds are prone to certain types of genetic ailments. That’s why breeders are trying to diversify the gene pool and create unique breeds that won’t suffer from genetic problems.