ExXB is right.
The published fare is that which you see on the screen at the time of your enquiry. If you look again a few hours or minutes later, the fare may have changed. It could have gone up or down as determined by the revenue management computer.
Revenue management is a very complex subject, and there is one such revenue management computer, based north of Nice, which is used by several airlines, maybe UA, cruise lines, hotels and other tourism related businesses.
On occasion, you may even be able to buy a premium cabin ticket for less than an economy ticket.
It is the nature of the thing.