Having hauled 60-inch bows through the woods for years, and now sub-50-inch bows for the past two years in the snowy, messy thickets game animals here hide, I never again wonder why many aboriginal peoples used short bows. A short bow is just as deadly as a longer one when the person doing the shooting is a short bow shooter, having learned to shoot the short bow from early childhood. In short-range hunting, being accurate per se isn't the biggest deal, as long as you are just accurate enough to hit the vitals of a game animal (six-inch groups at 30 feet can be shot with any bow). Being quick and maneuverable often is. There are situations where a long bow cannot be shot at all but a 45" bow has no trouble performing. Yet even some peoples living in wide-open semi-desert or steppe lands opted for sub-four-foot bows.
From the bowyer's point of view, short bows offer nothing but advantages. Finding clean 50" staves is infinitely easier than finding good 70" ones. Cutting, hauling, storing, working small-dimension wood is quicker and less energy-costly than utilizing big, long wood. If people find out they can feed their family with a 50-incher, they have no incentive to start making more ungainly weapons. And vice versa, if a longbow-wielding people have no trouble handling their bows in the local woods, and long bow-wood abounds, they have no incentive to start shortening their bows. As a rule, people stick to what has always worked and don't especially like change. Momentum at work.
Tuukka