I'd venture a guess this is,quietly, in retaliation for the increase in # of passengers permitted on USVI boats. It's been on the books since '95,not enforced. I'm also of the opinion that the gub'mint is looking for any nickel they can find.
From what I have been reading in the local media, it seems the tourist season isn't quite what they would like it to be and quite frankly, I think the government coffers are feeling it.