Body shots are indeed very useful given the right context and technique.
One reason you don't see them used more often in real fights is because generally in real fights there is some sort of emotional component (anger, fear, or pride usually) and therefore the striker is trying to hurt the "person" they are fighting. What you may or may not have realized is that we as humans most closely associate individuals with their face.
For instance, if I said the name Hugh Jackman, the first thing that would pop into your mind would be his face. Even If I said a member of the opposite sex who you might more strongly associate with other anatomy parts like Shakira or Dolly Parton you would think of their face first.
Hence, when people want to do damage to a person's persona, they generally seek to damage the face or head region.
You have to realize that most real fights aren't between formally trained fighters, and even among formally trained fighters it generally takes a little while to break their tendency to "head hunt" while sparring/fighting.
In a real situation you also have to take into consideration clothing (if it's winter and the person is wearing several thick layers of clothing that will absorb some of the force of your strike), the opponent's size relative to yours (the body is a bigger target sure, but also a more massive one), the fact that you may only get one chance to surprise your opponent with a strike and you never know what their ability to take a shot to the body is), that striking to the body never completely renders an opponent unconscious (and therefore truly unable to continue fighting), and that it generally takes more knowledge of striking skill and accuracy to take someone out with a single body shot than a single head shot.
Again, I'm not saying that makes body shots a bad choice, they can ba great if you know how to really throw them, pinpoint targets, and either hit hard enough that no matter who you hit and what they are wearing a surprise one will put them down, or you use them only when you are sure they will be effective (and you don't need to completely render your opponent unable to think/continue to fight back).
That's my two cents anyhow.