I dislike like the "why do you want this job?" question because, unless I'm unemployed and really needing a job, the fact of the matter is that I don't know if I want the job. Interviews go both ways. I'll need time after the interview to consider the experience and try to predict whether I'd be happy working there.

Unless your company is doing something extraordinarily cool, chances are your product is not enough in and of itself to attract many if any developers on that basis alone. What will attract people is the quality of the work environment, the quality of the people, and the amount of money you can offer them. That's really the gist of it, and during the interview the candidate won't have exact knowledge of any of those factors.