They are easier trips to prepare
Once you choose your boat, itinerary and cabin, you have 80% of the trip prepared. Just transport them to the port, and if you feel like it, what you will do on the different scales if you decide to explore them. There are different ways to organize excursions in each port. From doing it with the shipping company itself (more expensive but with less stress), with external agencies, or for free. In any case, you take the stress out of conventional vacations, since you will not have to balance flights with hotels, transport, reservations ...