The only reason I can come up with, is that the CDC is providing a way for revenue sailings to begin sooner than those that have to go through the test/simulated sailings process. (I know, why would it matter if cruises already aren't resuming until July at this point, since the cruise lines will move heaven and earth to get those test/simulated sailings done by the beginning of July?) The more I read, the more I'm convinced the CDC is going to do everything it possibly can to destroy the cruise lines.
At this point, unless they rescind the CSO, or clarify that restrictions do not apply to vaccinated cruises, nothing else they say matters as far as I'm concerned.