If he finally turns his play around in year...?...4? then what - you won't be able to pay him like a starting veteran left tackle and pay Donald and everyone else. So either Robinson stinks for 4 years and is released or he takes 4 years to develop and walks because we can't pay him. Either way - we lose. This is the crux of the problem with drafting players with 'potential' like Robinson, Quick, etc.
You need rookies who are ready to come in and start and contribute right away to keep your roster affordable or you'll never have a chance.