I have always found it odd that a player from their back to sit up to get a range of mobility to pass, see imminent contact/player pressure coming, and generally be in a more stable and comfortable position, yet the player on the floor on their stomach can never really get a similar position without travelling.
It would seem to me that most hustle plays would have people diving face and chest first toward the ball and floor, rather than back first 😉 Back first tends to be a result of a broken play where someone ends up off balance or already on the floor and flailing after a ball.
Not really a reward or punishment, but if I clumsily fall down on my back side and have to fall back to keep control of the ball (because I'm also clumsy) I can sit up. If I put my body on the line for a loose ball and floor burn my knees, hips and chest to get possesion of a ball I now get to lay perfectly still in a nearly impossible position to do much from.
My biggest concerns with these plays is player safety. When a player is sitting up almost no one dives on them or at the ball. When a player is prone on their belly there is almost always someone diving in or on second to try to tie the ball up. (IME)
*As officials I think its important that if contact happens to a player laying on the floor or diving at the ball I think its important that we get a foul call. Not just call for the tie up to reward the hustle on both sides.