Those were the only reasons I could think of - comfort, which is key on these longer and flat stages, and puncture/durability, which is usually better with wider tires as it spreads the weight more when the tire roles over a stone or bump.
I was not concerned about the added weight, since most of the other bike parts are so lite nor about the aero, since that really only comes into effect above certain speeds and/or in solo, time trial riding where you are not benefiting from riding in a pack.
Certainly neither weight nor aero would seem to be a concern given how many of the riders are using both front and rear disc brakes, at least on the flat to slightly hilly stages.