At least three Roman Legions are known to have had a boar as their emblems: Legio I Italica, Legio X Fretensis and Legio XX Valeria Victrix. X Fretensis was centrally involved in the First Jewish–Roman War, culminating with the destruction of Jerusalem and the Jewish Temple in 70 AD. In addition, it was stationed in Roman-occupied Judea for centuries and was involved in numerous other acts of oppression against the Jews. By one theory, resentment of this Legion's boar emblem, which came to be identified with extreme destruction and persecution, partly accounts for the deep-rooted traditional Jewish aversion for pork. (The Bible does not single out pigs in comparison with the many other unclean animals whose flesh is forbidden; nevertheless, in actual Jewish culture pigs are clearly singled out for a special, highly emotional loathing, of a kind not directed at other unclean animals)
So, the Jewish dislike for pork and pigs may be in part because the Romans were huge assholes two thousand years ago.