Do you really think the OL would have blocked with the same focus and level of intensity for Zeb that they did with Brown? WOW! If Zeb had stepped foot on the field, he would have sucked all the air out of that OL and we would have been looking at a repeat of UT and TAMU.
It is a real shame that you and others don't seem to understand that some players (not necessarily starters) are extremely popular with their teammates. The players KNOW and SEE who are busting their tails day in and day out. They know who deserves a chance to play, and the know who gives them the best chance to win. They are motivated to help those players succeed.
IMHO, the team resents the fact that Zeb was given the reigns when Doty went down because it was Brown who had busted his ass during the spring, showed out in the Spring game, put in extra work over the summer and fall, lost the necessary weight to make him even more mobile/effective, did everything the coaches asked, and as per many of Beamer's statements throughout the year, 'just makes plays when he's in there.'
The OL and the others on the team simply HAD to have a closer bond with Brown than with Zeb. Similar to the situation we faced under Sparky Woods with Steve Taneyhill - a backup known as a gunslinger, but with enough confidence in himself to take risks that others would not take. The players rally around players that like - especially when they show out once given the opportunity.