I think I have figured out why Harry and Hermione never happened.
It's because J.K. Rowling isn't so great at writing about romance. I mean she's a great writer when it comes to action scenes and overall adventure. But when it comes to couples and romance she kind of fails. If you think about it, Rowling seems to have just taken the main characters and slaped them together without much of a great build. Some may argue that Ron and Hermione were always bickering and arguing and that they were hiding their true feelings and other blah stuff like that but in reality the people who always bicker never end up together. While although Ginny may have always liked Harry, he never seemed to show much interest in her until much later for no apparent reason.
The point of these books weren't suppose to be about who ends up with who, it was about a boy trying to save the wizarding world from an awful wizard.
So the next time you're feeling a little sad about how the series ended just remember that these books were first and foremost about friendships, courage, and the power between the good and the evil. Not love. And besides, there are plenty of fanfictions and your imaginations to make you feel just a bit better.