These guys are either not paying trading fees, or they write them off as a cost of doing business. I think their strategy is to get the price lower, then buy a lot at the lower prices, and make 10%-20% on the Ask side.
There are always an equal number of Buys and Sells. It takes one of each to have a transaction. If the price goes to the Bid, that means the sellers are more eager. If it goes to the Ask, it means the buyers are more eager.