Not feeling the need to go left-on-left
Between Ryne Stanek, Hector Neris, Bryan Abreu, Rafael Montero and Ryan Pressly, the Astros have five relievers that are incredibly effective at neutralizing lefties.
At times, Dusty has shown his old-school way of thinking and overcomitted to the left-on-left managerial style. He's tried to avoid with his his hitters and been overly reliant with it in his bullpen.
The Astros bullpen is dominant as constructed. Even with a healthy Blake Taylor or Parker Mushinski, Dusty doesn't need to go to a lefty just because a left-hander steps into the box. Trust your best arms to do their jobs.