Pure physics.
The blades are spinning at the same speed so they throw the grass out at the same speed.
But the Gator clippings are smaller so have far less momentum thus drop earlier than the longer clippings.
If you can not visualize this, consider throwing a 1/2 lb quarts rock and a 1/2 lb of loose sand.
The single rock will go a lot further than the sand.
An experiment I did many times with my students using a mouse trap catapult.
It always amazed me how many times some needed to do it before they would believe the results.
Physics as a stand alone subject was dropped from the sylabus some time ago.
Next to biology the most important thing you can teach people as physics is the description of the real world.