desmei – everyone boarding a cruise in the US is subject to the US rules.
rob – whilst I agree with your criticism of the cruise lines, I would mention that the P2P sub-category has been used for tours for many years – long before the cruise lines were going to Cuba, and was so when such travel was subject to specific licenses, not general licenses. So tht is OFAC viewed them, too.
With regard to the record keeping, it is a good point that the requirements for P2P are more than for other categories, though “Individuals may rely on the entity sponsoring the travel to satisfy his or her recordkeeping requirements with respect to the requirements of paragraphs (b)(1) through (5) of this section.”