Because the tailiband had already gotten what little usefulness out of him they could, and he had become nothing more than another mouth to feed and not even useable as cannon fodder since there was no way they would trust him with any type of weapon.
Trade him for some of their leaders and probably a substantial amount of bribes? Helluva deal for them.
Bergdahl told the Taliban that he could help them get 5 of their buddies sprung from Gitmo.
Yup - Bowe probably didn’t even want to leave his jihadist buddies. They were likely done with him, and got the pleasure of turning on him and sending him back to the America he hates, and getting back their 5 big guns. Helluva deal is right - this has to be more than the usual Obama stupidity.