sometimes I think some manufacturers deliberately make their pants too long so that you need to pay extra for someone else to alter them, thus keeping tailors in business.
with sleeves generally the problem is the opposite, the sleeves can sometimes be too short. I know there was a fashion for three quarter length sleeves, but then it makes your arms look too long lol.
I am not sure what dummies garment manufacuturers go by or if my body is just dispropotionate! I do know that I am a size larger upperbody than my lower half though.
There wont ever be a fashion for one leg long and one leg short though sometimes you get dresses with just one sleeve that are assymmetrical.