Making trains go where people aren't relieves the pressure on ever increasing prices in populous areas. People will have a realistic option of living in cheaper areas.

AND it allows real estate speculators to get a much higher rate of return when they build up cookie cutter neighbourhoods in cheap land that is soon to be linked up by rail.

Both a good and a cynical reason for this behaviour, which is why I don't think you'll ever see it change (no matter where you are).