Exactly this. Vaccines don't prevent COVID in every instance, but they greatly reduce your likelihood of severe COVID/hospitalization/death.
DCL is going to have to weigh the potential consequences of dropping a vaccine mandate (primarily whether their onboard facilities can provide adequate care for more severe cases) against how much business they may or may not lose with a mandate. I would go out of my way to book a cruise that required vaccination, especially traveling with kids. I would choose that over other cruise lines that didn't require it, if all else was equal, and I can safely say that's true of the majority of my friends as well. I know there are others who feel differently, but my overall point is we just don't know to what degree the vaccine mandate financially impacts Disney. And in the end, we have to KNOW that's what the decision will be based on... $$$.
I wonder if Disney might mitigate the financial risk of unvaccinated passengers by offering a discounted rate for vaccinated guests, to compensate for the potential higher costs of having unvaccinated folks aboard.