Assume that to and from the hub fills 90% of the seats. Airline wants to keep that premium price but fill last few seats so it offers lower cost seats for people who fly from nearby airports. because the marginal price of flying these people is low, it adds to the bottom line while protecting hub prices.

I am flying LAX-YVR-China/China-YVR-LAX in business class for $2000!!!! less that the YVR-China/China-YVR flight. Go figure.