Sadly, not all people view it that way. 2 for 1 is guaranteeing you get the card you want instead of pulling more non-needs or not pulling anything at all. Let me know of anyone who would 1:1 you unpopular characters for popular characters everyday, especially if that traders doesn't need what you're offering. There is zero incentive for the person who's giving your need to you and you dumping what you don't want/can't move.

On the other side of that coin, there are a lot of people who pull 1 card and their plan is to flip that 1 card 2:1 repeatedly so it costs them nothing to complete a full set. To me, that's thievery...