What are companies expecting when they ask this

OK, so, in this site where companies post job offers for deveopers, there is always this mandatory question you have to answer before sending your resumé and the question is "Why are you interested in this particular job?". I've been answering this with "Because I'm hungry and I'm forced to work", which it's totally true and plain honest. Now, how would you answer this when all job offers are pretty much exactly the same?

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