Anyone who doesn't need to trade right now is free to place ALO orders, not cross the spread, and collect a few fractions of a cent in rebates. The fact that most traders choose not to get paid to do this should suggest to you that maybe you are incorrect about the need to trade right now.

I have no idea what you are talking about with "buy and sell orders without attached prices" (market orders?). You are correct that HFTs probably do not provide enough liquidity for Bill Gates to immediately liquidate his entire portfolio. So what?