With the agency model, the Buywise discounts are probably a big hit to their income--losing 15% means losing half their share of the price.
Or possibly, the publishers demanded that they discontinue it; it's possible that Apple & Amazon's "nobody is allowed to offer lower prices" contracts would clash with FW offering discounts and micropay dollars. FW may have worked out something where they stopped offering new Buywise subscriptions rather than canceling all their existing ones (requiring lots of refunds, and possibly lawsuits).
It's possible that the big 5 publishers will insist their content be removed from *all* bargains, and FW is anticipating having to make refunds, and is aware that they won't be able to effectively sell new Buywise subscriptions that only work on part of the site. And they may not want to bother coding the site to have it only work on some content.