Community college is different, people attend various community colleges in order to save money, to get ahead while in high school, or when they are trying to work their way up to a 4 year institution. The reason that multiple school transfers looks bad is because it shows a lack of ability to figure out whether a certain school or situation will be a good fit for you. If you have transferred multiple times in college without a good reason like family concerns or money, then adcoms can't be sure that you aren't going to be "wrong" about which medical school you choose. The goal is to admit students who will be able to complete their medical education while at the school.