Uh... why would they do that? He was selected because of his love and appreciation for the source material, as well as being a brilliant and capable fantasy writer himself.

He was selected (reported by him) for the eulogy he wrote for Robert Jordan on his blog. At the time he hadn't published "thousand pages" books. Though he later did, concurrently with writing the final Wheel of Time books (themselves thousand pages tomes).

And having read both of those authors, I really couldn't accuse Sanderson of being as long winded as Jordan. Sanderson's chapters (even in his long books) are bite sized and very comfortable for me, since that means I only remember the chapter number and don't use a bookmark. (often upward of 70 chapters for his Stormlight Archives series, which means less than 15 pages per chapters)

It should also be noted that Sanderson writes taking into account that readers can probably use a wiki to remember things, while Jordan keeps repeating things. Those books (while only a few months apart) weren't written for the same iternet era.