Yeah, I'm not saying I can see exactly what they see in him but there has to be more to their regard for him than just his short-term utility and performance which is not as bad as people think for the role but still very fungible. Does that mean he couldn't still be DFAed? Sure. Was it just a matter of not wanting to lose the depth (and lacking many options in AAA, especially if Nelson stayed a starter)? Maybe.
Regardless, hard to imagine him making a playoff roster or staying on the 40 in the off-season, but he is cheap and controllable if they think he can be another Matt Moore - which really took some time - or Ryan Vogelsong, or even just a viable 5/6. It's pretty amazing he hung on to the roster spot even as they went with a six-man but the various injuries and options allowed for it.