This isn't about the CDC "not working with the cruise lines!" This is just as much the cruise lines leaning on magical thinking and not doing anything to work with the CDC.
The Conditional Sailing rule does not prohibit sailing from US ports. But it does require lines to operate test cruises that demonstrate the required safety protocols, including distancing, port excursions, entertainment, dining, the whole bit. They have to be crewed sailings, and the test cruisers cannot be employees coerced to go, or people paying to go.
The lines have dug in about doing test sails and want to just load up with paid guests. Most lines haven't even filed their proposed safety protocols to support arguments to do so.
At this point, the cruise industry has had the sail order for months. They have chosen not to do anything with it, aside from ask for it to be modified, and hope that vaccines mean a full return to normal (and they won't). So this reflects on them, rather than just the CDC being "mean." There is no reason for the CDC to just remove all the conditions, and even removing some when the lines have done nothing would be a weird move. The CDC is not going to remove all rules around buffets and distancing and testing, full stop no. You can get the virus and spread it while vaccinated.