The other side of the coin is baseball is fucking weird, and weird things happen in elimination games. The Astros figure their best bet at knocking the Sox out is McCullers, and why risk a Game 5 where things could go sideways. This way, even if the Sox beat McCullers tomorrow, Houston is thinking "We still have the advantage in Game 5 as we are going back to our place."
I get it, but hopefully the Sox can take advantage tomorrow.