Two things come to mind: expected changes in the jet stream (with strong tailwinds, I once flew SAN-ORD <3 hours gate-gate), or the fact that the excessive block times were more often than not unnecessary and leading to poor utilization. On that flight in particular, I would think that the airport would not be as busy during the late evening hours, meaning less taxiing traffic being sent the long way over the Alpha bridge, and hopefully less traffic coming in on 9L/27R.