Princess does a southern Caribbean itinerary that calls on Trinidad. (Last year the Royal docked in Tobago). It's like New York City in Port of Spain, really congested. There are probably a few reasons this is not a port called on very often. 1. The port is small and very dirty. 2. There aren't any good beaches there. 3. There's a very limited amount of excursions offered. When we were there we did the Botanical Garden and Angoustura Factory. It was a great tour. 4. The island doesn't do a whole lot on tourism, oil is their main source of revenue. 5. High crime rate, although we never felt threatened. 6. The more "touristy" area is too far from the port and you're not there long enough to reach it.
I'm glad to see our tax dollars being well spent on chartering a cruise ship to use as a hotel.