why do guys like girls for their body and not for who they really are?

In the long run, we usually like girls for what they do and say, more than what they look like. As long as you are not fat, I will enjoy an agreeable person that enjoys sex, over any sort of beauty.

As guys mature and realize that certain personalities are better for long term relationships it changes.  However particularly with guys we are driven with our natural desires toward women we find physically attractive.  Women are more often than not are quite guilty of it too as less attractive men are far more likely to be friendzoned than an attractive one.  

Because physical attraction almost always comes first. People are allowed to have a preference. Would you rather a guy lie to you and cheat on you with someone that he thinks is physically more attractive?