Its quite simple really. During childhood the body can 2 of 3 things.
Grow a big body.
Grow a big brain.
Grow a big penis (you can subsitute breasts for the girls).
We tiny people didn't get the big body.
OK, now for the serious response.
Short limbs do make it easier with regards to leverage with lifting heavy weights.
Maybe in the genetics department short people are winning out. Smaller bodies require less food, heart doesnt have to work as much to pump blood, etc.
I think the PC term should be efficient people rather than tiny people.
Oh, and the stats are that between 5'7" and 6'2" is the norm for men.
I'm 5'6" dammit!