That Clinton (or Biden) would be better than Trump is a VERY debatable position. Very few people have exactly the same values. So when the differences between candidates is in degrees and not in directions, i.e. how much war/racism/xenophobia/lying/corruption/sexual harrasment is OK instead of whether any is acceptable at all, then a lot of people who “ostensibly share your values” are going to choose differently than you. Particularly choosing to either not vote or vote for one of the minor parties.