Sometimes (often enough, I think) the point is someone has something I've been wanting and I have something he/she wants to trade for and neither of us has the cash free to put up. In that case, one or the other of us is willing to do the down-trade in order to get what we want now while it's available and while I/he/she has the opportunity to do so.
The desire to get what I want now (and while it's available) will often outweigh the fact that I can get more for mine in cash $ than his is worth. Then I have to try to find what I want for sale (not always easy).
Despite appearances, both parties usually end up feeling it's a win-win.
Or, did I miss your point?
Show me the data