As with all interview questions, what is the real question? Here they are saying they don't want someone who is going to spend a year with them, building hours before leaving for somewhere else. You simply need to convince them that they are your dream employer.
If the interview was at BA, this would be easy. If you pitched up at Ryanair it might initially seem more of a difficult job but there's still loads you could say, like, how you always wanted to fly the B737, how it would be great to fly a young, modern, well maintained fleet, how the stable roster patern would fit well with your lifestyle, how you and your other half have long talked about moving down to the Mediterranean and RYR would be well placed to offer you this (once you've joined you can always "change your mind").
And thats just off the top of my head, you can think up something for any airline. The interviewer isn't an idiot and will know you're most likely bullsh@tting, but that's the game HR wants us to play.