If you not only ask people their preferences, but also ask "Why?" when you get answers, then what they say will match their actual preferences less well. Because they will be less willing to say preferences if they don't have followup reasons prepared. Because they have some reasons for preferences which they don't want to say, and others they don't understand well enough to say.
(If you follow only preferences which people volunteer to tell you, without being asked, that will match their real preferences even worse.)
You might expect that if you ask people their preferences and follow them, you're being super nice and treating everyone wonderfully. And then find they don't think so. I think it's an interesting issue.