Let's begin with a few assertions.
First, that Gameday was originally destined for a September 16th date with the respective fanbases of Florida and Tennessee at Knoxville. It's a traditional favorite of everyone on the Gameday crew, who historically hold great sway over where they go for the show. In fact, asserting this is just repeating fact; until Monday, that's where Gameday was in fact headed.
The second assertion we'll make is that for the most part, the talent decides where to roll on the weekends. Until this year, that's been the case, even with the strange visit up to Boston last year for the FSU/BC game, a place that didn't exactly reek of traditional tailgate. (It's Boston, and yes, we know, the parking is hell up there.) They usually make the calls on where to be, even when the game they're appearing at doesn't sync up with ABC's coverage.
The third assertion we'll make is that ABC/ESPN/Commandante Mickey/Cthulucorp completely and utterly put the kibosh on that practice this year and has gone full party-line with its college football coverage, meaning the game of the week--the one ABC hypes full-bore across its many-armed beast of networks--will unfailingly be the one they happen to cover. Which this week will be Nebraska/USC, which OMG JUST HAPPENS TO BE THE GAME OF THE CENTURY11111!!!!
Auburn/LSU is the Game of the Week! Unless it's on CBS, of course.
The fourth--and the one where we're playing a complete Miss Cleo role here--is that Gameday's crew was overruled by ABC/ESPN programming people, and that the Gameday crew sits less than thrilled with the decision and the infringement on their power to decide whom to cover and where to be on the weekends. No super-inside sources here, no major gossip, just a hunch that the suits allowing market-share decisions to drive coverage of a sport spanning at least four major networks and a countless regional ones likely irks them just more than a bit.
Don't take this as an anti-corporate screed, or some knock on ABC/ESPN/Gloved Rat/Cthulucorp, either; this is, by nature, what they'll do to improve their ratings and market share. It's more of a guess at the power dynamics between talent and management in the Sportstainment! division of things over there. Maybe Trev quitting and going to work with Bloo doesn't look so crazy in context, now does it?