Because Shawn Merriman made Long his B****!.
IMO the smart money would be to franchise him. No way will we get a better LT for 2013. I dont care if we overpay, we have the cap space and its not my money. The Pats franchised Wes Welker. No way is he playing up to salary, but they had the cap space and he is better than not having at all.
Tagging Long might be the way to go. See how he plays next season and go from there. But I would also have a back up plan in place to replace him if he doesn't play any better than this year.