He was rushed. Saw a video of bystanders yelling, “he’s got a gun!” moments before the first shot. He knew he’d been made and likely rushed the shot. Add to that he probably wasn’t well trained and likely drugged up and you get a miss. I also think he may have hit a teleprompter or something else between him and DJT.
I wonder how effective it would be in this situation if a bystander took a small mirror or their smartphone and used it to distract the would be tango with reflected sunlight in his face. But then again he wasn't just aiming for Trump. SOB was trying to spray as many rounds as possible into the whole stage area Mumbai style. He got up to 8 shots off before he received a .300 Win Mag cranial enema. The sunlight would probably help mark him out for the SS and SWAT snipers trying to get a bearing of where he is at...