An upvote is not about rewards. Or at least not only about rewards.

An upvote means that you support the author and his/her efforts for writing a post.

I was referring to people that comment hoping that they will get upvoted. These people have 100% VP because they do not upvote anyone, they usually do not post, and they just comment in a regular way without even bothering to read one line of the author's post.