The walls on both sites sold out ages ago. From what I saw there was maybe 100k up on BF and 50k on BTCT. The BTCT one sold out slightly earlier (but was smaller). I've no way of knowing whether all of the shares sold at that price were actually DT's.
DT has to balance risk/reward. He's having to break his contract to put up any sort of significant walls at all - and if his bid gets over-bid by 1 million+ shares then he could end up on the line for significant difference to get the naked pass-through shares back to being covered. As he's only making at most a bit under 2% on the actual sales there's no incentive for him to gamble too wildly trying to meet demand.