While NFL and NCAA football games look nearly identical, there are significant differences. Terminology is different, schemes are more complex and, of course, the level of competition is much, much higher.
This is why teams are often on the lookout early in the draft for players who are "pro-ready." While having a high ceiling is ultimately more important, there's a lot to be said for a prospect who can step in and contribute right away.
Whether it's because a player is physically developed (as guys such as Saquon Barkley and Quenton Nelson were in 2018), versed in a pro-style system or has the football IQ and instincts to make a smooth transition, some fit this bill more than others.