The SEC is about to go to 16 teams. That makes winning the league even harder. If the Playoffs don't expand to a point where 4-5 SEC teams have a chance to make the tournament every year being a coach in the SEC is going to be even harder than it is now. It's already getting to the point where 3 years is considered long term for a head coach.
Would a guy like Venables or some other "top" candidate want to walk into that? It would have to be mainly for the money because I don't see Oklahoma or Texas walking into the SEC and immediately dominating and whoever is coaching either of those teams is going to be under a microscope.
Lincoln Riley has a better chance to succeed at USC than he would long term at Oklahoma. He'll probably get Caleb Williams to transfer to USC and have a QB ready to go. Heck, maybe DJ would go home too.
I think you are likely right about the SEC angle, but I think also USC is simply in a position they could dominate the West coast and become a perennial playoff contender. Way too much talent is out that way, and the PAC is ripe to be dominated by a dynamic offense.