You could also build a big, spherical... let's call it a planetoid base... with a huge, huge weapon that could obliterate planets.
Deflect that, Obi.
My theory for why everyone fights defensively: they like their body parts. And you can easily lose some with a sharp sword if you don't know what you're doing, so why risk with a feather-light-cut-through-with-no-resistance lightsaber...?