He probably should not have picked Yellow.

Red is the only one with a car, because he is the only one who needs a car, as he does not work from home or within walking distance of his home. Presumably there are entire cities of other Grumblecampers, countries, governments, etc. But these guys just live in a tiny town between a desert and the ocean. I guess if they ever need to leave they can just ask Red to take them somewhere. Grumble cities are probably much more fun than the cities of the people on the other continents. They tend to be cramped and impersonal. All the buildings in a Grumble city would be shaped like the people living in them, possibly stacked on top of each other to make high-rises.