I have a theory about that, as I’ve long thought other, lesser league’s dunk contests are often better than the NBA’s.
The lower you go down from the NBA, the more guys you get who can just jump/dunk, but can’t do anything else. The D-League, the NCAA, other random leagues, etc. are filled with Gerald Greens, guys who can jump out of the gym, but don’t have the whole package. Lots of times, I feel like these are guys who always got by on their freakish athleticism and verticals, so they never had to develop the other dimensions of their games, or they're not strong enough, or too short, but boy can they can dunk.
In the NBA you’ll have a dunk contest like this (just throwing some made up numbers out here):
Gerald Green – 50 inch vertical
Eric Bledsoe – 42 inch vertical
Terrance Ross – 44 inch vertical
Harrison Barnes – 40 inch vertical
Damien Lillard – 44 inch vertical
But in lesser leagues, you have
Joe Blow – 50 inch vertical
John Blow – 48 inch vertical
Joe Nobody – 50 inch vertical
John No Game – 48 inch vertical
Plus fan's expectations are usually ridiculously high for the NBA, while incredibly low for all other dunk contests. So it's easier for the NBA to disappoint and other leagues to give you more than you expected.