When you’re paying, you’re not buying the fuel nor are the salaries directly affected by one person is paying for riding a train.

What you’re describing is called “marginal cost” and reducing this is the reason why the economics of any large scale business is actually working. You could argue with these marginal costs, but you’d be entering a completely different model/domain of economics. And no one uses this model which is abstract/non-abstract in any aspect that happens to make your point valid.