This isn't always true. Storms don't always crawl in with plenty of lead time. They can pop up out of sunny skies in minutes. That's likely what happened here and why they pushed off when they did.
I assume it's nothing more than the notification process not working right due to some network issue. That's why they come through sometimes, but not others.
The 3-4 day market is not just a bunch of first time cruisers. There are plenty of regular and seasoned cruisers just taking the long weekend approach to vacations.