As you're interested in a career in banking, plenty of reasons should spring to mind, and if they don't you should consider choosing another path!
Often students are attracted to the intellectual challenges and high-profile nature of the dealings of the finance world, the fast pace of the work here, and the rewards on offer, all of which are very valid reasons for applying to a bank.
But they're also valid reasons for applying for jobs in other parts of the finance world, so make sure you explain why you want a job at a bank, and in your chosen area in particular. Perhaps you're keen for the broad and deep financial training and prestigious experience that only a leading bank can offer?
Your interviewers may also ask if anything puts you off banking. If you have any real doubts, an interview is not the place to air them, but it's a great idea to show that you've considered the difficulties the industry is currently going through before choosing to make an application.