Well....since you can't think of any, it must be true.
Much of the problem with the transitioning from QB in college to the NFL is there is no way to bridge that huge gap. Pitching in college and pitching in MLB is a good comparison IMO. Many kids drafted out of college and most all of those out of HS spend time developing at club level before being called up, the NFL doesn't really have that. So....they have to take their lumps early and learn or sit a few years. Most of the QB's drafted that are considered ready struggle early or end up on a sorry ass team. Look at Luck for instance, he was going to be the next Manning, problem is he has very little talent around him. Dak wouldn't have been nearly as successful on the Jags, jets or Browns and getting drafted by any of those 3 is a death sentence. Carr on the other hand, on a team with some talent, same for Cousins.
I'm gonna go off the reservation for a minute and put myself in the line of fire. Most of what is wrong with the QB position is something people are afraid to speak about. In the last 10-15 years the media and the usual talking heads have whined about not having enough black QB's so they have forced the issue. Problem is most of the one's in college are GREAT athletes that run a versatile offense like the spread or whatever you want to call it. There isn't a lot to read, some but not nearly as much as pro ball. Tons of defensive formations, stunts, disguised coverage and so forth. College coaches run the off. they do because it's exciting and hard to defend but it isn't preparing many of the QB's, regardless of color for the typical NFL offense. Right now the NFL is in a transitional state and one in which it is going to have to decide what it wants to do.
They can't run a college offense because the QB's cant take the punishment at the level and many of the coaches have already spoken about certain QB's having to learn to stay in the pocket and stay downfield. I could go down the list but you get my meaning (think RGIII).
As a disclaimer, I am NOT saying that black college QB's can't learn the NFL system and be successful, I am saying that aren't be asked to in college. But if there coaches have them thinking that they are, that's all they need to hear.