Not sure how this is "disingenuous." It's not like they're trying to trick you. The fares are published. And the price swings are due to market conditions as reflected in various algorithm inputs. UA charges what they think people will pay at any particular point in time.

More generally, I often find UA's fare structure frustrating but I try not to spend too much time worrying about it. Either I pay the fare they're selling, or I choose another airline, or I don't fly. I don't see much point in adding "angry" to the list of menu options.