There is no logical explanation for Sanchez getting the start. At least not performance wise.
We've played 12 games this season and Sanchez has looked good in maybe 3 of them (Bills, Colts, Rams).
It's painfully obvious that this kid is what he is. Maybe a serviceable backup who can come in and win a game or two in a pinch. That's the future of Mark Sanchez. He is in no way the future of this team.
Sitting this kid for a quarter and a half isn't going to suddenly make some magical switch flip on.
Rex had a chance to send a real message by either moving on from the Sanchez era permanently, or at least going with McElroy for the final 4 games and make it clear to Mark that he'll be involved in an open competition for the job next year since we're basically stuck with him. No more handouts.
Instead, we witness the same coddling of Sanchez that we've come to expect from this front office.