I'll bet the main reason for delaying cancellations is this. Every day they delay is another day they have your $$$ interest free. As soon as they cancel, they have to send cash to those preferring that over FCC. Simple.
Currently Norwegian has cancelled cruises through April 11. I know there are at least 2 cruises scheduled to leave April 12. Has anybody booked on a cruise leaving April 12 heard anything from Norwegian yet?