The PH went from an excellent charge video, excellent fast shooting, to copping a lot of criticism for not making a third shot. Though likely the buffalo was quickly dying anyway. The second shot I think was a pass through the buffalos heart / lungs. It just takes some time to bleed out. A third shot might not hasten anything.

A lot of people have a \ "keep shooting until it's dead" mentality. A lot of experience professional hunters know it can take some time for a big beast to bleed out.