Cruises to nowhere are no longer allowed.
For anyone interested in why, I found this explanation on another site:
The PVSA was revised a few years back to allow cruises to nowhere, and they are still legal under the PVSA. What has changed is that CBP has ruled that while crew on foreign flag cruise ships that call in US ports need a crew visa (C1/D1 depending on whether they are joining/leaving in the US or not), crew on a foreign flag vessel doing cruises to nowhere would need a H1-B work visa. The H1 work visa is more difficult to obtain, costs more, and has more financial and legal responsibilities placed on the "sponsor" (cruise line). The cost for a cruise line to get these visas for a thousand crew for one or two voyages (sometimes separated by months) would not be cost effective.