successful train lines in Japan are all built between CBD and some spots / attractions. Odakyu: odawara / hakone, Seibu: chichibu, keiou: Takao, toukyuu: Nikko / kinugawa, nankai: Takao.

Tourists spots are usually in the mountains and the CBD is near the sea. And residential area is developed between them along the lines so the trains carry bidirectional passengers to work or relax on the same line, higher utilization keeps ticket fare low.