Interviewers ask "Why are you applying for this position?" because they want to gauge whether a candidate's motives, interests and goals align well with the requirements of the job. In anticipation of this question, the best approach is to prepare a response that includes a few key interests that align specifically with core elements of the job duties.
If a candidate has to lie or answer in a disingenuous way, the job may not actually be a good fit. However, if the interest is genuine, the goal of an effective response is to convey true passion for the role of the position. It is also helpful to expand on the answer to address reasons for wanting to work for the organization.
For example, when interviewing for a newspaper you could respond that you are a recent journalism graduate and are eager to start your career in a position where you get to work on various stories and apply your online technology skills to promote articles online. You could say that you have long been a fan of the newspaper and would love to work for such a recognized publishing brand.
In answering, the key is to highlight challenging or reward elements of the job. Avoid making money or personal benefits the focus, as this often turns off employers. Additionally, don't give a vague or incomplete response, such as that you "really like working with people."