I think what this particular question is evaluating is the understanding that you've internalized the norm of academic continuity; i.e., you know that as a doctor, major academic resources were invested in educating you. That comes with a responsibility to pay that investment back to society in intellectual work. The question is trying to get you to ask yourself how you envision doing this form of service, and why.
This question is asking you to confront your mortality in a way. What do you hope to leave behind? How are you going to move the profession and your chosen patient population forward? You have to have preferences to compel you to work with some people over others, on some specific type of problem (vs all of the other kinds of problems that can happen to a person).
In other words, if you say you're interested in everything, you're really saying nothing particularly stands out to you—which is rhetorically the same as saying you're not interested in anything. Whether you choose to be interested in the intersection of psychiatry, innovation and social justice like me, or you choose to be wrong (I'm only half joking)—you get to choose what it is that you want to teach us, your future physician colleagues and collaborators.