I think a lot of the reason may be (and I don’t claim to know why) that as a tender port with typically long, long tender times, this port has a much higher percentage of passengers either waiting on board to depart, or ones who simply bypass Grand Cayman and don’t get off at all.
I have been to Nassau many, many times. But I will still get off because it’s easy. Grand Cayman? Nightmare to depart. Never getting off there again unless something really changes.