While it can be random bad luck, you avoid the expression of these deformities by not inbreeding. However, inbreeding is common to produce purebred animals as well as in puppy mills. These things can result in a beautiful dog, that at some point gets bombarded with it's poor genetics. My grandma's dogs were like this- great pets until about 8 years old- they went completely blind, deaf, had hip issues within a few months of one another (they were brother and sister). While these things on their own aren't bad, they also suffered from a number of other issues I can't remember, and all of these issues were genetically based (not medically, since you can have something happen that causes the dog to go blind or deaf). I just remember the vet telling her to put them down because it would only get worse- and that it was a result of inbreeding. A commonly known one- purebred german shepherds generally have early onset hip issues because of how their legs are bred and how frequently they are bred with other purebreds (meaning limited genetic variance).

Now all these seem not-so-cosmetic, but that's because the above mentioned are a lot more common. Only in the last while (I'd say 50 years) have we seen dogs like this that are so horribly deformed because of how they are bred. Believe it or not, some people actually intentionally do it to create "ugly dogs".

This is just to the best of my understanding, though. The "bad luck" scenario is more likely to come in to play when you just have a minimal amount of issues show up- For example, a little of puppies was given to our local shelter- all were fine but one, who looked much more like the mother's breed and was completely blind. Blindness is one issue, and likely was a genetic "accident". But as with my Gram's dogs, the prevalence of several comorbid disorders that all happened at once- that is a sign of poor breeding and not just an accidental thing.

Hope this makes sense!