I think this is the most likely answer, and he's also got seniority and more knowledge of our system.
Lukas Van Ness looked like a 6th round pick throughout training camp and preseason games. Now in two real games he has looked pretty good. Conversely, Rasheed Walker looked like a stud in the preseason but really struggled at the start of the Atlanta game.
The reality is that some guys don't practice well, either because they don't put in the effort or it just doesn't show. Whatever the case may be, we know that some guys are just gamers. I'm always in favor of rotating your guys through to find the right fit. I couldn't give two schlitz if Rhyan looked bad in the preseason. If he knows the plays, get him out there and see how he does.