Rumor is that they had to put their thumb on the scales (i.e. tweak the model) to get enough sellers to sell to them. In other words, if paying what their model actually thought was the right price, not many people sold to them. Instead of saying "our division's whole business model won't work, you should fire us", they tried to cut the margin too close, resulting in losses which got the CEO's attention to the problem.

This kind of thing is difficult to confirm from the outside, of course. But that they adjusted the model to pay more towards the end is pretty widely known.