I'd tend to say that it is probably because they haven't yet crippled their AI bot with the same dark patterns (trying to make you select insurance, paid selection of seats, additional luggages, rented car at the airport) as they do on the website.

Airlines websites could be so much simpler and quick to use if they weren't designed to be full of traps.

Don't expect that edge to persist indefinitely, they are in the adoption phase.