In a way it's a rhetorical question but in another way it's not. Sure some will move there for a job but I'm sure not everyone is there just for work. Why do people put up with all that? Is it just the dream of living in NYC.
For me, I started to age out of it which made it less worth it. But it's more than a dream or "fomo" - it truly is the most enjoyable place to be in the US. I visit nowadays and it's just as magical as it used to be.
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:
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:
Having said that, yes, it could still well be (too lazy to figure it out properly) that inside this city core the Paris Metro is still more dense than the Underground in London – but on the other hand beyond that, where the vast majority of inhabitants of the whole urban agglomeration of Paris live, you have similar problems regarding radial travel as elsewhere:
https://www.ratp.fr/plan-de-ligne/img/rer/Plan-RER-et-transi...