Metro is heavy rail. It’s basically a system of electric commuter trains that go back and forth through the DC area.
So most of the people who use this greater DC train system are Federal workers and workers for businesses that lobby the Feds, contract to the Feds, cater to the Feds, wine and dine the Feds or kiss their arse in some other way. The train riders are all tax eaters, some directly and some indirectly. Those trains would be ghost trains if the DC tax spigot was cut off to half the current flow