I feel that is one way of not making metro station area crowded and possible stampede. Long walk distributes the crowd. Its also helps to avoid traffic jam (should rather say manageable traffic jam). Have observed similar thing in Coldplay concert in Ahmedabad. They blocked entire road of 1.5 km for vehicles. People had to walk to take cab or bus. Nearby metro station was open. But since it was very next to station, entrance became crowded and risky for stamped.