Why has eating pig been forbidden?

Describing what is distinct about pigs, Hadrat Khalifatul- Masih IV ^rta explained:

However many herbivore animals there are, of them there is only the boar which has been given the “blades” of carnivores, and they are teeth that advance and are as sharp as a sword. In the Punjab they are referred to as sword. To wildly attack is in their nature. Many animals have been given means of defense, for example, antelopes and mountain goats have been given horns. However, ferociousness is not in their nature. All experts of the world are witness that if they ever attack it is in their breeding season. At that time some wildness comes into them, but they cannot be called ferocious, nor are their teeth like carnivores that rip and tear, as the Holy Prophet ^sas described. But boars have such teeth. So it is likely that the Holy Prophet ^sas forbade against ferociousness, of which the Holy Quran has made the boar an example. Under this category, all beasts that do not respect animal life, rather it is a part of their nature to tear them and cause them harm, they are forbidden. It has specially been said not to eat the meat of those animals that have teeth that tear, and some birds have also been mentioned.

(Urdu Tarjamatul Quran Class #20; Surah al-Baqarah, 2:175–181)

Hadrat Khalifatul-Masih IV ^rta explained:

I am personally convinced in that it is ferociousness that is the actual reason, and their being forbidden is an objection against ferociousness. That is why the attention of the Holy Prophet ^sas went from carnivores to birds as well. There is strong objection against ferociousness. If ferociousness is found among any meat-eating animal, then it is the wild boar. It is most dangerous in the jungle. If it sees anyone, it is inclined to attack. attacking and destroying are in its nature, it destroys crops as well. In a Hadith, the Holy Prophet ^sas said that you will see the scholars of that time as pigs and monkeys. They are called pigs because it is in their nature to destroy. Rather than converting people to Islam and sowing new plants in the garden of the ummat of the Holy Prophet ^sas, they destroy even those who are here. So the culmination of ferociousness is also found in them, issuing verdicts of death with no hesitation. So it is these characteristics of ferociousness and destructiveness that stand out in this animal, and the Holy Prophet ^sas strongly objected against it. He ^sas included this in the way he understood the meaning of the Quran, that is why such things are declared haram. Carnivores kill, but they do not destroy. So rather than give the example of carnivores, the Holy Quran has given the example of boars. They show ferociousness in crops as well. The rest of the animals eat according to their needs. They dig and scratch, eat of their choice, and fly off. But boars plow the crops with its plow like blade, and it destroys the entire crop. I understand that these are two fundamental things against which there is an objection. The meat of similar animals have also been declared as haram, and the Holy Prophet ^sas counted them under the same category.

(Urdu Tarjamatul Quran Class #20; Surah al-Baqarah, 2:175–181)