Maybe Gil can weigh in on the thinking behind why interactive cards are left out of the 2p game. I would think that the 2p game would be the perfect place to use them and NOT so much in games with 3/4/5p since you might be picking on the person who isn't winning. In 2p, since hurting your opponent means that it's directly helping you, I just found it to be a curious decision.
Having played it a bit and seen some of the cards, I think the reasoning could be in what you mentioned - just flipped around a bit:
The interactive cards are a way of the players who are behind chipping away at one person in the lead. The person in the lead would likely not want to go for them, since they are already in the lead and picking on a weaker player (say P1 picking on weaker P3) is leaving an open door for a third/fourth/fifth player (P2) to just strengthen their position by being out of the conflict. (not hurt by the move - P3, or not hurt by opportunity cost - P1)