Re: Once again....
It's easy for us fans to judge who should start based on preseason games, but we haven't seen all the practices. I wasn't hired to coach the Steelers (and with good reason). Tomlin is the coach, and we have to assume he knows what he's doing.
One possibility is that when a younger player is pushing for the starting spot, Tomlin wants that player to take the spot in mid season, rather than the end of training camp. This would put all vets on notice that complacency will cause them to lose their starting position.