There's a philosophy, originating from the book One Straw Revolution, I believe, of not disturbing the soil layers. So they prefer to smother weeds and such with layers of things like straw. Newer practitioners use cardboard and plastic.
Unless you have access to lots of smothering material, and lots of time to wait for them to work (up to a year, sometimes more), then digging is a quicker method to get crops in. True, it does spread the top soil level all over the place, but you're also adding compost, manure, etc to bring back the soil's tilth. And you're not digging beyond 2 ft down, so its not a drastic disruption really.
Some say worms get killed with digging and rotovating, but they can be killed also by simply digging with a hand trowel to insert a plant (though not to the same extent).
It's all personal philosophy and preference. Some actually find digging very soothing and enjoyable. Others rotovate for speed or inability to dig.