Why? Surely experienced programmers, who are being asked to do the work before giving a cost estimate, know the difference between a project that will take 48 h

Why? Surely experienced programmers, who are being asked to do the work before giving a cost estimate, know the difference between a project that will take 48 hours and one that will take five years. Plus they charge, if I read correctly, a maximum of $500 so one would think they wouldn't take anything that's even remotely out of that $scope.