They spend billions on new stations that are way, way bigger than they need to be. They spend billions tunneling in order to placate rich people who'll sue if they use the cut and cover method, which is much cheaper.

That's not cost effective. Paying way too much for an elevator due to construction industry graft is not cost effective.

But putting in an elevator at a fair price so that disabled people an mobility impaired people and elderly people who just don't want to risk falling down stairs will ride the subway more? That's absolutely cost effective.