[dengnan]

For cost consideration? Those poles are made of bamboos which is probably the most inexpensive materials in ancient China and it's easy to get. The shape of the poles is exactly the same as the raw materials. So people only need to cut the bamboo and that's it. No need to do any further work. Bamboos grow very fast and straight. This makes it have very low defective rate.

Imagine there was no plastic, no composite wood. You had to find a large piece of wood to do even a small design. Plus, if there was really a needs for alternatives, there was Chinese weelbarrow [0].

http://www.lowtechmagazine.com/2011/12/the-chinese-wheelbarr...