§ 545.058. DRIVING ON IMPROVED SHOULDER. (a) An operator may drive on an improved shoulder to the right of the main traveled portion of a roadway if that operation is necessary and may be done safely, but only:
(1) to stop, stand, or park;
(2) to accelerate before entering the main traveled
lane of traffic;
(3) to decelerate before making a right turn;
(4) to pass another vehicle that is slowing or stopped
on the main traveled portion of the highway, disabled, or preparing to make a left turn;
(5) to allow another vehicle traveling faster to pass;
(6) as permitted or required by an official
traffic-control device; or
(7) to avoid a collision.
Why doesn't Reed Bates operate his vehicle on the shoulder? Because it's not really legal (ed. error... see comments below). He would have to be constantly moving on and off it, like Barry Sanders running through a defensive secondary. In Bate's case, they'd probably arrest him for it.
Besides, read the operating intent of an improved shoulder (1-7). Does that sound like a travel lane to you?