Why do you want to join [ENTITY REPRESENTED BY INTERVIEWER]?
You can both compliment the hospital [or group] and make yourself look good by embracing the qualities extolled in its Mission Statement. This is readily available online and is usually displayed on its website; you should identify with it as part of your interview approach. You can answer this question by telling your interviewer that those values are the same as yours and are prominent in the way you practice.
"I know that the values here are the same as my own. In my research, I particularly like your community interaction, your embracing diversity, and always putting the patient first. This is the same professional mindset by which I think I can be the most productive and happy."