The Merc ones don't just go in a single arc like their twin wiper brothers... They stretch out to reach close to the edges of the windscreen and then retract when they are headed towards the top of the windscreen giving a nice field of view.
A Single Big wiper in the middle of normal origin would be limited to the height of your windscreen, thus it would not be sufficient to reach across and clear the drivers view totally. Unless you can come up with something ingenious like the above method .