Basic electrical theory: Electric current flows in _circuits_. When the equipment ground is bonded to the neutral at a single point only, there is no closed path, and thus no circuit. With no closed circuit, current cannot flow.
This ideal of single point grounding is only achieved when there is a single customer on the transformer. With multiple services connected to the same transformer, you have multiple point grounding of the electrical system, and thus closed circuits on the grounding electrodes and grounding electrode conductors, with current flowing through these parallel ground circuits. Plumbers have been shocked cutting water pipes after the neutral connection has failed.