That's for new buildings.

Most people don't live in new buildings.

Fair enough. Do you think it's easier to add some vent fans or retrofit a building gas->electric in every flat? It's not as easy as it's made out to be. Buildings were designed with sufficient electric service given the utilities available at the time. Buildings with gas have undersized electrics. In other words the service (transformer etc.) is likely inadequate. A massive retrofit from gas to electric cookers would be insanely expensive.

Actually, I think gas->electric is the easier one quite frequently.

Simply because adding vent fans can be a physical impossibility because there's nowhere to vent to. There's more living space on the other side of the wall (in your building or an adjacent building) so you can't vent directly outdoors, and there's no duct so you can't vent anywhere else either.