But in practice runs empty most of the time, is commonly delayed by any problem on the line or station, and operates on a very limited schedule.

In the US, because the US is very bad at building public infrastructure. Or, lately, building anything.

The ability to carry people is worthless if no one wants to use it

People generally don't want to use it because we design everything exclusively for cars, so cars are more convenient. At the cost of increased risk of death, increased travel time, increased land cost, etc.