There are 47,000 people in the city (who are on the hook for the bill).
Of those 47,000, only 5,400 have chosen to get the service.
The remaining people, who chose not to get the service, are the overwhelming majority.
You don't have to read minds, you can read TFA. Most citizens have chosen not to get the service.
There's a flaw in your logic here - you are quoting 'people in the city' in one breath and then comparing it to 'households' in the next breath. Exactly how many house holds would you expect to see have more than one subscriber?
I'm not sure exactly what the average household size is to use for this, but assuming that's 4 (2.5 kids and all that) then the uptake is more like 45%. That's a pretty good number even compared to top commercial offerings. (How many are rented and not allowed by landlord or stuck in other contracts?)