It would've made more sense for them to keep Jimmy G., but craziness prevailed.
I suppose Kraft told BB, "look, even if we franchise him this year, he walks next. Only guy who was tagged twice at QB was Cousins, and he eventually walked. Jimmy G isn't starting until Tom says he's done, and I can't see that for a few more years. Plus, his agent is Brady's, so he's out to max out both contracts. We can't match what this kid can get as an FA, so get what you can." Of course, they should have realized it when they still had Brisset and dealt JG last spring.