Less motion if you bring the round up from underneath and roll it into the ejection port....rather than coming in from over the top. Coming from the top, there is virtually nothing to index on and as you can see, the shooter fumbles the rounds getting the them in. There is also lost time as the support hand comes from the eject port back over the top of the receiver and then has to wrap underneath to rack the slide.
Coming from underneath, the round is held between the first and fourth finger. The hand can easily index against the forward edge of the trigger guard while the two fingers guide and roll the round into the open ejection port. The support hand then moves forward a couple of inches, engages the slide, and racks it home. A lot more efficient.
Just sayin'......