Ah, pork. It's a human favourite: bacon, sausage, hot dogs... yum. If we love it so much, why doesn't it appear in our pet meals beside other human favourites, beef and chicken?
One. Fat content.
Yes, unfortunately, one of the reasons bacon and hotdogs taste sooo good is because of its high fat content. Fat is an important macronutrient for humans and animals too, however the high concentration of pork can lead to over-eating that particular macronutrient. The amount of pork we'd need to include in our pet meals as the protein content would have the terrible trade off of too much fat, leading to weight gain, lethargy, joint pain and worse!
Two. Nutritional deficiencies.
Once again, humans lose out. Pork is not a complete protein, meaning it does not contain all of the essential amino acids that humans or dogs need. This incomplete set of amino acids mean our pet meals would need to be bulked out even more with other protein sources like beef, chicken or fish. This makes pork essentially 'filler', especially because of reason number three.
Three. Digestibility.
Pork can be difficult for some pets to digest, which can lead to digestive problems such as diarrhoea and constipation. Especially at the rate dogs eat their food, the meat doesn't have time to properly digest and break down, not only potentially blocking the digestive tract, but also meaning the body can't access all the nutrients that are available in the meat.
Four. High cholesterol.
Yeah, cholesterol. Can you believe that's something dogs have to worry about? It's not, unless your pet eats a high fat diet. The reduced nutrients, higher fat content and non-bio-availability of the meat, can cause issues with cholesterol. This higher level of cholesterol can lead to a decreased quality of life through obesity, pancreatitis, obesity or liver disease.
Five. Allergies.
Worse than high fat and a lack of digestibility and bio-availability, some pets are allergic to pork! Symptoms of pork allergies can include itching, hives, and vomiting. This can disrupt their immune system, irritate their skin, and lead to discomfort. Basically, not worth the risk, especially considering everything else on this list. 
So, even though pork is a fan favourite, it doesn't serve our goal of increasing the nutrient intake of your pet, satisfying their palate and honouring their evolutionary process. Look, we'll turn a blind eye if you give your dog a bit of leftover bacon or pork chop every once in a while, but we want to offer you the best nutrient-dense meat on offer.
