McCree has a robotic hand, that's also his reloading hand, I think sombra hacked his hand so he couldn't quick reload while he rolls, idk.. video games
Because its a Mechanic in the game, and lets just be fair, most things in this game aren't "Realitic" I mean frankly we have Zarya making black holes and Symmetra bending reality and your concern is that by hacking McCree he can't roll?