I'm gonna say it's cause Jansen hasn't pitched a lot, Blanton has, and you keep Blanton at a pitch count where he can pitch multiple times this week instead of have to have him sit out one game
Jansen has barely pitched lately because we have either gotten blown out or have been blowing teams out
I've questioned multiple moves by Dave (leaving Maeda in for Pence, Toles instead of Joc, not bunting with Enrique) and every one has worked so.. he might know the future