According to statistics, there are ~19 million people living in the NYC metropolitan area. In comparison, there are only ~2.8 million people in the DC/Baltimore metropolitan area, which is ~7 times smaller. Naively this means that those pushing for statehood for DC should also be interested in granting statehood to NYC, as well as the 19 other metropolitan areas that are bigger than DC. However this does not seem to be the case - we can find numerous articles on granting statehood to Puerto Rico or DC, but none about NYC or other cities.
Why is this the case? What makes DC unique compared to others? Do note that the issue of "no taxation without representation" could just as well be solved by merging DC into Maryland instead, so this cannot be the only argument.