"Why do you want to dedicate the next few years of your life working on this instead of something else?" If the answer is just because it pays more or the company is in a better location I think most employers would want to keep looking for someone that has different motivations.
I've never found that to be a great idea. In all honesty working on a stack in one company is much the same as another asides from whether management is an ass or whether they're paying you decently - that kind of thing. A passion for the company's mission is just nonsense IME - sure, the person might in theory like the idea of better traffic management (or whatever) but at the end of the day that's not going to keep them warm inside in the same way being treated with respect and an extra £20k/pa is going to, or in the same way that having their kid go to a local school and their wife or husband working in the same area is going to.
You've got things that keep people bought into a company and passion... I'm not seeing it as a big part of it, especially considering so many people are going to lie about. People are too alienated from the product of their work for it to be meaningful.
What I have found reduces attrition is if you train people in house, if you treat them properly, if you pay them decently - that sort of thing. Which is basically what people are telling you when they say they're interested because of the money, they don't know enough about the company to say much else.
Passion for a role, now that's meaningful - but it's not really a company-specific thing, it's more a work-ethic thing.
If you're the type that needs personal validation such that you would knock a candidate for saying something like "I need money, you guys are paying in money", then you simply shouldn't ask the question. Of course, people love to think that they have a highly tuned bullshit detector, are immune to blatant flattery, etc. The problem is everyone thinks that. We are all susceptible to these things and we need to make sure our process is such that its not biased towards people who are particularly good at telling you what you want to hear.