As an advertiser, if I see a site with placements that are only available via direct buys, and the advertisers cycle through there quickly without staying around for a while, that's often a sign of a poor performing placement that they tested and moved on from.

I'm not clear on the specifics of their inventory, but some of their placements are available on the Google Display Network, and presumably exchanges as well. So I'm not sure if the inventory with the $20k min. buy overlaps at all with that to reach this sort of conclusion.