Free running and coasting periods are generally long in case of main line services. Distance between two station is longer in main line service so free running is long in main lite service. Coasting perform a natural deceleration of a motor when the power is removed in main line service distance between two station is long so there is more time for stop the strain at station then power is removed earlier and coasting is long.
Speed decreases naturally due to friction, the weight of locomotive at coasting.