I don’t have a ready article to link to but there might be some from when Sandy hit in 2012. Basically: there isn’t enough safe space to park all of the trains

I don’t have a ready article to link to but there might be some from when Sandy hit in 2012. Basically: there isn’t enough safe space to park all of the trains when they know the system might flood. They could just stop trains where they are but then they have to get people to/from the trains and there’s a risk that any given train may develop a fault and block the line it’s on. It’d be better if they could just park in the train yards but several are at sea level.