The NFL Draft and free agency are vastly different experiences for players. As incoming college prospects, they have little authority or autonomy over their immediate futures beyond having given permission to teams to claim their rights. Whoever drafts them, that is the only team that they can play for until that team elects to part with him.
The instances are few and far between of any rookies exhibiting any kind of force over such situations, the obvious known examples being John Elway and Eli Manning, both of whom forced trades to other teams, the Denver Broncos in the case of the former and the New York Giants in the case of the latter.