They're fired at the targets each round was designed for i.e. fleshets were designed for armor penetration so they fire at armor vests, buckshot, ball & buck were designed for impact devastation so they fire at ballistic gel, etc.
Besides this film is a police training film to teach cops what's out there that can defeat their vests, etc; not a sales advert film from the ammo companies
Yet the ballistic gel was different each time it seemed, and why not fire the buck and the flechettes at the same target for a comparison, rather than one at a dummy (incidentally blowing the vest off from my memory) and one at a vest on a board?
The buckshot does this to a 3 inch thick block of gel, but the buck and ball does this to a foot of gel, I'd rather see the comparison of both in a foot of gel*.
*Measurements made up, but seem roughly to the scale I saw.