This the parking space does not carry a marginal cost for the operator. Rather the problem with not driving is the lost marginal charge for milage.
Tokyo also has anti idling policies. Thus these car rental services will not want to be associated with such an illegal activity.
Tokyo you "must" have an assigned parking space - but in other areas, this is not a requirement. Right next door in Chiba-shi and Saitama there is no requirement to provide proof of parking space.
Anti-idling is also 50/50.
From personal experience I can assure you Saitama requires a registered parking space, I registered it myself. The dealer would not release the car to us until we could prove the registration.
I don't think car parking gets a rent subsidy in Japan. They don't have the US-style zoning with required parking spots per square meter, and when you buy a car you have to prove you have a monthly parking spot (which can be quite expensive due to the land cost)
> Where else can you hire private space in the centre of a city on an hourly basis for the rates that car sharing companies charge
As the article mentions in passing, cybercafes/manga cafes cost around the same as car parking, and you get a private booth, WiFi, sometimes free soft drinks etc. Some have showers and other facilities. http://www.live-matsuya.co.jp/anchor/images/anchor_01.jpg
There must be a subsidy here, because these cars are being driven elsewhere (low mileage != no mileage), and the comparison of the car rental cost as being similar to that of the cybercafe implies there is no additional cost of parking. So the parking is free, but it's quite valuable, as demonstrated by their exploitation of it; hence, there's subsidies here somewhere.
Anyway, I just looked up some actual prices for central Tokyo:
* Parking, 1 hour: 900 yen
* Car sharing, 1 hour: 900-1,800 yen (depending on car class)
* Cybercafe, 1 hour: 550 yen
So sitting in a car actually costs twice as much as a cybercafe