It depends, but yes it is not free. It is however quite cheap if you have a full car. So for example anyone going for weekend with family, highway is cheap and is MUCH faster then normal roads.

Japan also has a developed highway rest areas, you will often see people sleep in the car there, often whole families in vans that been outfitted for it. There is washroom, restaurants, sometimes shower and even hot spring, they are also clean, might have local produce being sold, alcohol etc

Here is a priceless use case for a salaryman from Tokyo. Get off work, get drunk with coworkers, get in the car with family at 10pm on friday. Car delivers you to the closest michi-no-eki to a ski resort and parks itself. Wake up at 6-7am, get to the resort by opening lift, grab breakfast at conbini drive to resort. There are lots fo places less then an hour off highway. Being able to sleep and being driven on highway would be incredible.

Company that delivers that feature in the family van will destroy competition until they can duplicate it.

If you're solo yes, once you're two people it tends to be on par, 3 or more car is cheaper. Every family I know owns a car. The highways are full of cars and trucks.