They wanted as much offense in the lineup as possible. They didn't play Julien at 3B because he would also have been bad there and Polanco has at least had reps on the left side of the infield. The gameplan was to bat Polanco and Julien at the top of the order, get the lead and then put in Farmer as a defensive replacement (moving Polanco back to 2B). Kudos to Polanco for filling in on short notice in the playoffs but using him at 3B is a terrible plan for 2024.
Personally, I would have put Willi Castro at 3B in that series and played Polanco or Julien at 1B to replace the injured and ineffective Kirilloff.