The problem with almost all public transit is that it converges on a center and branches out into legs that do not connect with each other.

This is the DC map:

https://www.wmata.com/schedules/maps/upload/2019-System-Map....

If two friends move to the outer edges of different legs of the system, then your travel time and inconvenience multiplies a lot.

It is the same reason Manhattan is so popular compared to the outer boroughs:

https://new.mta.info/map/5256

People in manhattan can go west, south, east, north anytime anyhow with few or no connections. People in the outer boroughs have to many times go via Manhattan to get where they are going.

Now take a look at a map of a good subway system:

https://www.tokyometro.jp/en/subwaymap/

Paris is another good one:

https://www.ratp.fr/en/plan-metro

You can get from anywhere to almost anywhere without having to go to the middle of Tokyo.

The Tube is okay, but still has the problem of the lines not connecting once you get out of a certain radius:

https://content.tfl.gov.uk/standard-tube-map.pdf