You aren't just filtering by who is willing to pay more, because willing to pay more is also indicative of how valuable that inventory is to the people buying i

You aren't just filtering by who is willing to pay more, because willing to pay more is also indicative of how valuable that inventory is to the people buying it. All demand is not equal. Some companies have very valuable business they can do with the inventory while other businesses have less valuable uses for it. The more valuable uses are willing to pay more, so higher prices means the most valuable uses get filled first.