Because we'd be neglecting the opportunity to upgrade at other positions. If we were talking college recruiting where you have a ton of scholarships and a much bigger roster, I'd say sure! Bring them all in! But this is the NFL where you have a salary cap, a draft order, and a 53 man roster. Can't take TEs in the 1st and 2nd round while you already have an All-Pro on the roster. Olsen could easily have another 3-4 years left in the tank. That's the majority of a rookie contract.