Why bother with heavier weapons?

They make you use your body a lot more.
You must compensate for the weight of the weapon - without tensing up - and still move in a lithe, nimble, strong manner.

Unless you work with a heavy sword, you are essentially 'playing'.
A lightweight wushu sword doesn't tax you much.
You can perform any manner of fancy moves that would be downright impossible and non-viable with a heavy weapon.

In a very real sense, a genuine sword grounds you: in terms of connection and in terms of its functionality.