Because you say so.
Whether the glove flopped around or not would depend on the stiffness of the glove. If that's a leather glove, and I think it would be, it's not going to flop around like a cloth glove. It seems a rather flimsy excuse for saying that cop is not Haygood.
The missing glove vs the Cancellare Photo is one of Many Facts. The timelines of the film'd together, Haygood? + Harkness, + Walthers are also rock solid Facts. This is why a 2nd Haygood on foot, deep inside the railroad yard, has Now suddenly been invented. And this invented Haygood 2nd trip into the train yard, also changes the timeline of the Darnell film showing this motorcycle cop. But do you question any of this? Silly question.
Getting back to that (L) hand, I do not see him holding a possible glove. Whatever he's holding has a circular shape and is flat on the bottom as held. If this guy was wearing a glove on his (R) hand, in your wildest dreams, would you think that object in his (L) hand was a glove?
So now we suddenly have: (1) Haygood making a 2nd trip into the railroad yard, and, (2) a claimed motorcycle patrolman's "glove" that is somehow shaped like a cylinder. ALL because I have proven "That Ain't Haygood"!