I honestly think PLD is the only guy that kinda makes sense for both sides. Bruins couldn't accept futures at the deadline given where the team was, and our needs were top 6 center and top 4 LHD. Kings aren't deep enough at LHD to trade away from that position, so I don't think it's that.
And you'd think they Kings probably aren't willing to trade any of the pieces in their top 6 given they're currently in the playoffs, but they do have PLD on the third line. So they trade away from an area of depth and get out of a contract they seem to regret giving to fill their biggest need, Bruins trade away from a position of depth to add what they see as a long term solution at center. Personally don't love the idea of trading for PLD but I see the logic for both sides.