They are selling transportation from location A to location B via an airplane. The specific airplane, assuming it has the features the customer paid for, is more of a technicality.
If they just stopped showing what plane would be used on the route, maybe they'd get away with using 737-MAX series.
If they say 'it's a 737-800 don't worry about it' and swap in a max every time, or 'fly with us on an airbus' and bring in a boeing death-tube after a purposefully misleading advertisement of a different service...
Terms Of Service only gets you so far. It's not a fraud-dodge.