I feel like all these urban-Japan examples are more "only in the most densely populated places" rather than "even". If demand is high enough then you can absolutely support multiple competing routes: they all get enough passengers to survive, and the denser coverage is beneficial. It's when you get a bit further out and into smaller or less dense areas that it starts to get tricky -- different private railways end up complementary to each other as they serve different suburbs but are the only railway for most of the places they serve.