OK! OK! Let me try to get this right.
I will couch this question in specifics. Suppose I would like to book an excursion to stingray city without using my cruise ship. Easy enough to do, but who insures the excursion. How does one know there will be sufficient life preservers and other safety equipment? And when the excursions boat or van breaks down, how does one get back to the cruise ship which is leaving faster than quicker? For these reasons we have avoided taking any but ship excursions in the past.