Jobu, looks can be deceiving. Take my word for it, my back is arched and erectors flexed so tight that they sometimes charlie-horse. Head is forward, not up. Maybe that's what LS meant. I took up to mean looking up.
Why? Safety, leverage, maximum recruitment, basic physics, biomechanics....
Conventional will hit your back harder, sumo will hit your hips harder. I pull sumo to spare my back strength for squatting, and because it's a shorter ROM.