I'm not big into politics, but I think it's the fact that Trump acts quite "immature" for a president. It feels quite... embarrassing, to be honest, although he did have my vote. Again, since I'm not into politics, my "liking of Trump" would come down to his likeness as a person, and Donald Trump is not an easy person to "like". From what I've seen (and maybe the things I've seen have been the result of media bias), he is stubborn, rude, unapologetic, overly confident, volatile, and not willing to admit when he does something wrong.
Are his politics good? I don't know. But as a human being, he's not an easy person to like. Especially considering how insanely rich the man is; he doesn't seem "for the people".
Edit: He also has very little credibility, in my eyes. This is a result of him being stubborn and not willing to admit to his mistakes. As a result, when he makes a claim, it's not easy to rely on him being faithful to those claims because he would just as easily blame things on someone else if he failed to come through.