Not unlikely? Can you point us to all the other times this has happened? You must know of several given your knowledge of how obviously likely this is.
When has "nothing will happen as long as we can carefully navigate our massive vessels around these critical pillars" ever been a trustable safety measure? Over the long term shit like this will happen if it the possibility that it happens is not excluded by other measures.
This is a public bridge 5 years in the making and who knows how long in planning, and people have been extremely lucky that it collapsed at 3am and not in the middle of the day. It doesn't matter at all how unlikely this is in a given time frame if the impact if it happens at any point in time is catastrophic.
It's not especially common, but the Sunshine Skyway Bridge in Tampa Bay is a famous example. Similar circumstances - it collapsed after being hit by a ship.
This is a public bridge 5 years in the making and who knows how long in planning, and people have been extremely lucky that it collapsed at 3am and not in the middle of the day. It doesn't matter at all how unlikely this is in a given time frame if the impact if it happens at any point in time is catastrophic.