I think the main reason this happens is that your application status is just one narrow column in a spreadsheet, and once assigned, the students don't go away after their deadlines. For example, ED1 kids who haven't yet been interviewed remain in the system, regardless of their having been accepted, deferred, or denied. It's good for the deferred kids who might still like an interview, but it would be easy for a volunteer to mess up and contact an accepted or denied applicant.
kid112 is right, interviewers are ready and able to help you out even after you've been accepted. Most of us won't try to oversell the school, just help you make the best choice for you.