re: Traction.
I think that they 'dared' to go to the left end of the bedrock for the science sake. There are rocks at that end that are higher and they probably thought that the rover could get an easier reach with the RAT on those. They might also want to work from left to right.
This area seems like a good outing of the crater... a more leveled way to the outside. We'll see. The rolling up of any crater would be the hardest, imho.