This used to be a standard practise even 20 yrs back on PI....leave the sign on the entire time, keep the aisles clear for the "express beverage service"...
Now, if the sign was on yesterday/today, perhaps they thought they might run into some unexpected turbulence from the frontal effects of the hurricane...just a thought....but 8hrs without a lavatory, if a FA had specifically stopped me from going, would have resulted in a IAM member having some extra work to clean up after my in-seat job.