Grand Cayman is surrounded by a large reef. Outside of the reef in Grand Cayman it drops off to around 15,000 ft. The reef protects the island and the underwater wildlife of the island. Also, Grand Cayman isn't a "poor" island that needs tourism.
The second largest natural reef in the world is the Great Maya Reef. It skirts the coast of Belize. It is also a protected reef and Belize will not destroy the reef to allow cruise ships with a 25' draft to get through. Also, there would be a world wide outcry if they did.
So: you not will see tendering to these two ports for a long time to come.
I believe that there should be a balance between commerce and wildlife and it can be done responsibly. However, in these cases I don't see a valid reason to destroy a reef in order to save cruise passengers from a few minutes of tendering.