Because a pig was always the easiest animal for people to raise, that very easily gets very big and heavy. Can just feed them scraps and garbage, and don't need to do much to take care of them, and they grow. So it was the most common animal for many groups of people to be farming. They didn't need to be a farmer, they could have any job, and also have a pig.
The reason the enemy religions all banned pigs is because they purposefully acted to starve all these people to make them more dependent on the church. When everybody is starving to death, they become desperate and they are more likely to accept these cults which pretend to want to help them. And a vegan diet destroys the brain and causes a dullness on the mind that also makes them more likely to accept the evil cults.
Every neuron in the brain, and every nerve in the body, are surrounded by a material called Myelin. The myelin protects the nerves exactly like insulating coating around a wire, and ensures that the electrical signals are transferred correctly and not lost. Myelin is a product created by animal fats and proteins, we get the materials to create myelin by eating animal products. There is not any vegan product that can replace this. People on a vegan diet for enough time, the myelin sheaths around all their neurons and nerves starts drying out and decaying, which leads the nerves to not be able to function correctly. Signals start shorting out, not making it to where they need to get to, or jumping between nerves so the signal starts stimulating other nerves which were not supposed to be involved. Leading to things like twitching and shaking which can be seen in any long-term vegan. Also can lead to things like numbness in the nerves, and slight paralysis of some small muscles. And also a constant dull pain inside the nerves that never goes away, this can happen any place in the body. And this is not only happening in the nerves in the body, it is also happening inside the brain. Every kind of process within the brain is affected by this, leading to the same kinds of problems of signals short circuiting and signals jumping across to other unrelated areas. Which is the same as having small seizures within the brain, and at the same time having dullness where brain signals are not always recieved by the sensor they are supposed to go to.
Imagine taking a computer circuit board, and soaking it in salt water so every trace on the board all start to rust away. Would you do this to your whole body and brain?