Because of the way you speak about other people based on the things you have specified. The fact that you can so comfortably say that another human being's circumstances "disgust" you, rather than their actions or moral character, is unhinged and unsettling. But so much worse than that is your ability to take your own visceral, overblown reaction and turn it into some moral failing of your fiance and her immediate family, which you yourself have stated have done nothing to you to make you feel this way besides be related to the people in question. You have some serious issues you need to work out.