There is a big long explanation as to why that Ron Sutton I'm sure could explain better than I, but in a simple form...having a high travel setup lets one configure the geometry to work best in all areas of a turn and the straights as well.
With a super stiff spring setup, the static geometry is what it is pretty much all of the time. You dial in camber to help the outside front tire contact patch, but completely give up the contact patch on the inside front tire.
With a front suspension that travels, you can maximise the contact patch on both front tires in a turn. Aren't two tires gripping better than one?
Watch this video to see how well a soft spring\big bar setup helps make a G-Body turn.