No matter how you think about it, pigs are a rather dirty animal. They are considered the scavengers of the farm (created to eliminate any waste on the farm), often eating anything they can find. This includes not only bugs, insects, and whatever leftover scraps they find laying around, but also their own feces, as well as the dead carcasses of sick animals, including their own young.
This in itself can explain why the meat of the pig can be so dirty or at the very least not so appetizing to consume.
There a a lot more cons than pros for eating pork, thus why it is forbidden to Muslims.