Because most of the bidders (according to the leaks) are financial professionals, not goofy little impatient daytraders, and might consider a bifurcated strategy of buying a large lot at auction for a fixed price, followed by a lesser but still substantial purchase at the exchanges at market price to immediately drive the price up and increase the value of their existing coins.
That shouldn't be that hard for even you to understand.
So if they put 700 at the buy price at stamp and click the Buy button, they're now a goofy daytrader?
I would understand them paying at a high price if this is a rare item being auctioned... but it's not... so I'm sure most of them are there for a chance to buy it at a discount