Gtown Green's move vs. a dribble move

[Nevadaref]

It is strictly a matter of what the rules say a player may or may not do.
The rules specifically prohibit lifting the pivot foot prior to starting a dribble. So that is why that is illegal. I'd guess that the rationale is that it would be too difficult to play defense, if a player could get a head start with his first step as he started to dribble.

On the other hand, the rules state that a player who is holding the ball, either before dribbling or after ending a dribble, may lift his pivot foot as long as he passes or shoots (or requests a time-out) before putting this foot back down on the floor.