You see more body builders at less than 5'10" because they most likely have a mesomorphic body structure which is better suited to building muscle and looking good doing it. I have one brother that is 6' and no matter how much lifting he does, he will probably never really look real muscular. However, my other brother who is closer to 5'6" or so, he can lift weights and in a matter of weeks he swells up and looks very muscular. There are three general body types:
Mesomorph: shorter bone structure, taught muscle build, good for weight lifting and body building
Endomorph: average bone structure, slightly elongated muscular make-up, better all around athletes (most quarterbacks and sprinters are this type)
Ectomorph: elongated bone structure, elongated muscles, mainly basket ball players, long distance runners, etc.