[jedberg]

Japan has zoning laws at the country level, and they are much more sane than local zoning laws. Basically, local zoning says "this piece of land can be used for one thing". Japan's laws say "this piece of land can cause a maximum nuisance of X, but it can have all these different things on it". And then it's up to the developers to decide if building a multi-unit building would more profitable than a single family home.