Justin Fields traded to the Steelers for a conditional 6th round pick

No you didn't; that was Lamar's sophomore season..lol. But in all seriousness, from the standpoint of actually throwing the ball, mechanics, touch, arm strength, etc, Fields was seen better in that regard, while Jackson was seen as more of a project.
Scouts (and you ) can be wrong. Jackson clearly is better than Fields and it has nothing to do with coaching.