> Airline apps have to cover shopping, booking, cancellations, seat selection, loyalty programs, check-in, bar code generation and scanning, and so on.
That may be true for some airlines (webviews vs native), but it is not true for many. Boarding passes are probably a good example. It's very typical for that functionality to use something like Apple Wallet integration, and also native widgets to upsell cross-sell boarding/seat upgrades, etc.
Passes already in the wallet don't require you to be online. But, what I meant was that there was additional code, thus additional size for all the functionality and ui related to boarding passes, whether or not parts of it don't work offline.
At least the airlines I've worked with prefer native code and UIs for any flow that's either revenue-producing, or likely to create issues on day-of-travel. They tend to use webviews only for things that don't have to be working to sell a ticket or board the aircraft.