I'm not saying there isn't room, I'm just saying that with limited space and a captive target audience, having three competing subway lines is incredibly inefficient, especially when you consider that there will be 1-2 lines that all three will service, while other areas won't have any service, given traffic patterns.

I'm not sure how this is in the interests of any city really.

Of course it is, it's quite common for many companies to compete with offers, and the local authorities choose the best one. But that kind of competition is not aimed at the end user, passenger.

NYC has tried that - the system started out as 3 competing companies, but in the long run, it makes sense to have one system with one set of management/employees