The CDC and other health officials don't control cruise ships' access to our nation's ports: state and federal elected officials do, and most of them don't want the cruise industry to die on the vine. After a few months, our ports will probably open, along with the rest of society, as it dawns on all of our leaders that we can't realistically lock down our economy for several months on end. I think a federal ban on lawsuits against institutions by people who get COVID is the key to society getting back to normal.
Just to clarify the No Sail Order is issued by the CDC and does control access. Under specific conditions, US code has CDC setting the guidelines. Some of that is in the CFR which the executive branch can amend, but some of it is USC law that would require congressional action to amend. I wanted to correct that statement so people wouldn’t think an individual governor could override the CDC no sail order (and the specific order notes that state nor USCG cannot supersede the instructions and rules). The president could replace HHS and CDC secretaries/directors but that would also require Senate approval for his replacements so in this one particular area health officials have more authority than normal.