I think it is b/c they have so stinkin' long to make a throw they can take their time....reset and make a throw..
And not relevant to softball...no time to add this extra movement....
I can't link to the video but if you go to the sticky thread in this forum under Model Fielding and look at the 4th video 5-3 you will see this happens in softball to...basically if you get a hotshot and the batter is not even half way down the line this little tap forces you to gather yourself and make a good throw