In many areas, the freight shares the same rail as passenger rail, so they need to schedule around those. It could also have something to do with the dock workers schedule or whatever, bridge opening and closing times up the line, there's probably hundreds of things that go into it. Pretty sure once they get something that works, they don't want to change it.

Train use was way way off last year (down 20%) but things like lumber, chemicals, coal, etc are still carried mostly by train across the country.

According to the CSX commercials, one train can replace 280 trucks using one third of the fuel they use.