So first off, his YPR is actually pretty low. Player Profiler lists it at 13th percentile.
My theory for this is that he didn't have particularly good QB play and, as a result, he rarely got hit deep in stride. Ball tracking is also supposedly an issue for him, and his hands are listed as a weakness as well.
Anyway, if you watch his highlights, you can see that a lot of his production was getting the ball behind or near the line of scrimmage and either housing it or getting a first down. And it's important to note that he had more rushing touchdowns in college than receiving ones, which indicates some dynamism in space. How much his lack of downfield receiving production is due to his QB is something I can't say because I didn't watch his team's full games.