As a somewhat naive traveler, I actually find this to be outrageous. The fact that "Amex does it, too" makes it only more sickening, especially since the Amex travel portal at first blush seems to not allow booking of basic economy at all. (BTW, at first blush, the Chase portal gives you no access to United basic economy either.)
I'm not sure whom to fault for this situation with American and these portals, but I sure wish that there were more businesspeople like the grocery chain in Europe that just took Pepsico items off their shelves because of price increases. At a minimum, I cannot see how not disclosing this in pitches for Chase Sapphire cards is considered at all reasonable.
Why would Chase and Amex have this issue with high-pricing on American if Expedia does not?