I can understand it if he really gets drafted top15 or so. Top15 nfl pick gets a guaranteed 13-15m or so, while now he only has a guaranteed 4.6m.
If he becomes a star he makes more in baseball but he first needs to get through 3-4 minor league years and then 3-4 minimum pay years depending how service time is manipulated.
Also while he can easily bust as a QB he can also bust in baseball, his hit tool is raw for a college bat and plenty of elite athlete have failed to hit in the majors.
He has a high bust risk in both sports and probably chose the higher floor.