A more practical answer too, would be that when an army went into encampment, they would need thousands and thousands of these poles. Enough to strip a small forest bare... And as mentioned previously what if they weren't encamped near enough trees to generate the poles needed.

Since the soldiers carried dog tents, the larger ones would have been transported in wagons... sure the wood took up some more space, and weight, but when you figure you're only adding a few wagons worth of supplies, its not that much in the long run especially compared to the difficulty and man hours involved in finding/generating the poles.