Because that would put the forearm in a position of pronation at that point, which means the pitcher would then have to supinate their forearm to get their palm facing the target. Supinating at that moment focuses the load on the UCL and may be one of the things that makes pitchers need Tommy John surgery.
Even those pics that you posted prove my point. The palm isnt facing third base in any of those and they are later in the arm path than cav’s is. My point has been made, at the point where his hand is in the arm path, his hand should still be facing down. There are no ifs, ands or buts about it. It is physically incorrect to have the ball facing any position but down/back until the arm is pronated, during an overhand motion. If the ball faces anyother way, you either 1) dont throw over the top or 2) have a major delay in your arm path. Try to throw a ball by turning it over at the bottom of your arm path. You will not have any velocity and you will place a ton of strain on your shoulder. The pics that I posted, no matter what point they are in during the arm path, prove that the ball/palm should be facing down or behind until the fore arm is rotated to throw the ball to the plate.
I’m not disagreeing with you about the position of the hand but I do want to ask you about what you mean with this statement. Are you speaking of the arm slot being “over the top”? If so, why is this a good, or necessary, thing?