Scottie Lago is around 6'1" or 6'2" and he usually towers over the competition. Most of you top pros are 5'9" or less. When you're essentially doing aerial acrobatics with a stick strapped to your feet, shorter is usually better.
"People say that marijuana smoking is going to get in the way of my career. I say to them that on the contrary, my fighting career is getting in the way of my marijuana smoking." -Nick Diaz
Im going more with the gymnast theory ... constant high impact on a regular basis tends to stunt the growth process ... Kooley is about my size at 6 ft and Ted Borland is probably 6'3 .. those are two more taller guys off the top of my head ... oh Corey Smith is 6'1 ish or so .. but still your original premise is correct most tend to be smaller