This question can be tricky, and should teach you to listen carefully to the question being asked. While running down the list of reasons you're suited the position may get a good point across and can help the interviewer assess whether you qualify for the position, it isn't exactly what they were looking for. Your interviewer wants to determine the reason/s you want the job in order to determine whether you are the right person for it. Being capable of doing the job and wanting it are different things, and these factors can affect your performance and how long you will stay in the company.