People who do not own dogs may not understand the necessity of dog clothes. Some will argue that if a dog has fur, why would they possibly need any other protection, especially the Pom who has that magnificent "ball of fur" coat.
It is different for many medium or large sized dogs. Many have been breed since the beginning of domestication to be outside dogs. There is still a debate over the exact time that humans began to domesticate dogs; the general theory is that it happened some time around 8000 BC. However, small breed dogs were breed a completely different way...to be pampered inside dogs.
The medium and larger dogs were breed over time for many things: protection, work (such as sled pulling) and rescue (as they could much more easily find a missing person than a human). Therefore, they did not need anything else other than their own fur.