The Student Room Group
Reply 1
its probably because body hair has weaker roots than head hair so falls out more easily. this hair is replaced. the length that it appears to stop growing at is probably the equilibrium where hair falling out is replaced at the same rate.

although i may be wrong :smile:
Reply 2
you are always growing all over your body.. you don't stop growing in any place.. as undry1 said, the hairs on your arms and legs stay shorter because they fall out more often, and are replaced.. not sure why they fall out.. maybe undry is right.. maybe it is best to google this :P