I would not assume that people necessarily have any reason, at least the kind that can be formulated as a statement about the world, like "this gives me good feelings," before you ask them why they did it. Of course, once you ask, they will come up with something, but it may be something that in fact had nothing to do with the fact that they did it.
If there's such a small chance of your vote making a difference in the election, you should be comfortable voting for trump.