Jennings problems are more than just between the ears. It's not like he can just stop shooting, pass all the time, and become a star. Players that can't score don't get defended at all. Jennings is walking a fine line between jacking shots to keep defenses honest, and being so bad at scoring that teams probably shouldn't be guarding that closely anyway. That's the real issue in Jennings game.
If Jennings were a more efficient scorer, he wouldn't be open all the time and would have more opportunities to make passes. Because he can't finish at the rim and is generally a poor shooter, defenses fade off him all the time. He takes a lot of dumb shots, sure, but he also take a lot of shots that the defense is actively conceding. Jennings just doesn't have all that many high end skills. I know we want him to be great, but there should be more honest conversation about what he can actually be better at to begin with.
Jennings is small, not very strong, and not very long. He's a terrible defender, has been even under good defensive coaches. He's not a great shooter. He's not an effective slasher to score. What Jennings actually does well is pass and take care of the ball. When Jennings had that huge start to his career, people presumed he had a ton of scoring talent. His career to date has shown that the scoring talent was really just a fluke.