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Why do Americans have to file taxes, even if their only source of income is from a regular job?
A couple things. First of all, most people's MAIN source of income is from their job, but they have others, such as bank interest, stock dividends, etc. So that income has to be reported with their wage income. The second thing is that most people have deductions NOT connected with their job. These deductions reduce income (and generate refunds). So it's in their interest to file.