Imagine the cost! Putting meters into properties now would be a massive task. What about all the converted places that are now flats?
Putting them in new builds might be an option, but it's too lucrative to charge an imaginary amount to pay for the power station to risk losing income by charging for actual use (unless they put an eye watering cost on the price of a unit of water, - then the whole system is outed as just a income stream for the government).