Stopping a large portion of the interested parties from being able to place buy orders was a large factor I think. It was such a gut check to momentum that by the time they could switch to other brokers the enthusiasm has cooled, also because in the mean time it was much easier to manipulate the price back down.
I'm convinced in an alternate reality where the clearing houses weren't able to almost completely stop buying that it hits 1000 easily. But you give everyone 5 days to see people fortunes evaporating and suddenly reality sets in.