Why did the City Hall Subway in NYC get shut down?

It was closed in 1945 for a number of reasons including:

It was not heavily used. Since it was a local station, people would just walk the short distance to the Brooklyn Bridge station which was/is an express station.

Since City Hall was built on a tight curve, it could not work well with more modern cars that 3 doors on the side of the car. The original IRT cars had a door only at the extreme ends of the car. Those doors would come close to the edge of the curved platform at the desired spots. In order to use newer cars the IRT and later the City had to use cars with extra door controls so the center doors would not open. The station would definitely not work with todays subway cars.

When the platform extension programs began it was determined that the City Hall station was just too close to the Brooklyn Bridge station ( the curve of the station didn't help).

Don't apply a general statement like "since the subways are known to be one of the ugliest in the world". The stations that have been refurbished in the bashed 20 years are so happen to be quiet decorative and attractive. Examples: 81st St-Museum of Natural History on the B & C lines, the Canal St station (Upper and lower) of the N, Q, R & W lines, the Coney Island station on the D, F, N and Q lines - just to name a few.

Another reason it won't be reopened (except for the Transit Museum Members only tours) is - security. It is just adjacent to the City Hall building.

Other systems may be prettier, but none are grittier. Some of those ugly stations have been serving nobly for over a century of hard time. The system carries three miillion riders a day. It is open 24/7. And works, not perfectly, but very, very well.

The station you described you can get a peek at if you take the downtown #6 train from the Brooklyn Bridge station. It turns around via a loop that passes through the station and the ride is part of the regular run for that purpose.

London, Paris and Moscow are actually less advanced than New York. We have a 4 track system that runs all night, and we feature the most advanced automation system ever implemented, truly robotic trains on the L.

platforms are to short for the modern trains. its a real beauty of a station. the transit museum runs tours on occasion.