Well, obviously AA is assuming that people who want to buy a ticket four days before departure are willing to pay $600, and people who want to buy a ticket 21 days before departure are only willing to pay $185.

They might be right or they might be wrong. One thing is for sure, and that is you cannot assume everyone else has exactly the same travel budget you do, nor can you demand that AA sell you a ticket at a price you name. That's just not the way it works. Even on Priceline where you "name your own price", the airline has the option to turn down your offer, just as you have turned down AA's offer of a $600 ticket four days before departure.