I know it adds cost and complexity, but Jet2s cost basis is no longer just that of running a low cost airline model.
The airline component still very much is. For the likes of Thomas Cook, even TUI to some extent the airline has always just been a means of supplying the holiday business really. Similar in a way to how short-haul feeds the higher yielding long-haul for full service carriers.
In Jet2's case, despite some of the comments above, I don't agree even now that's the case. They still have a very economical, cost conscious and reputable airline operation. Yes it's more tailored to the package holiday clientele, but the airline itself is still very much a focus of the whole product.