In the terms and conditions most people never read, the cruise line has the right to cancel a port. When they do, it usually last minute. If they do, make sure they refund the port charges you have paid. It's always disappointing, but when we've been on a cruise that had a port cancellation, it's always been for a good reason.
Port Stanley, Falkland Islands: It's often removed when bad weather or the Drake Passage threatens Antarctica itineraries, so cruise lines protect time in the Southern Continent. 50% of cruises that are expected to visit are cancelled, so know this before you go.
Dutch Harbour, Alaska: This is a remote, rugged cruise port located on Amaknak Island in Unalaska, Alaska famous as the top US Commercial fishing hub. Ships usually dock at the Industral City Dock located 4 km from the town center. Weather is a huge factor for cancelled cruises.
Santorini, Greece: This port relies on tendering and there is a lot of wind. Another reason is the number of ships in port. Caps are put on cruise ship passengers visiting the island. Some days there are too many ships and the island doesn't want another 5,000 people from a huge ship. If you want to visit Santorini, go on a small ship, not a mega ship. Your chances of visiting would be much better. Azamara cruises stay until late in the evening so the masses of people from the other ship are long gone!
Tarshavn, Faroe Islands: I loved this port. We were fortunate to visit. Weather would be the problem as it's in the middle of the Atlantic between Scotland and Iceland.
Georgetown, Grand Caymen: Georgetown lacks a cruise pier, so ships anchor offshore and sometimes cancel preemptively if winds or swells could strand passengers ashore.
Isafjordur, Iceland: This port has frequent high winds and a relatively small dock, leaving larger ships dependent on tendering until planned dock renovations happen.
Lerwick, Scotland: Depending on the size of ship you are on will either dock or tender. Winds are a problem with tendering so this port gets cancelled frequently.
Cruise lines private islands: They aren't actually private islands, but pieces of land the cruise ship purchases and locals manage the private beach. Most are tender ports so again, it depends on the weather conditions.
Summary: I love the large ships for the different entertainment venues and more activities. However, the smaller ships get into more ports. The best example is cruise lines that dock by the Tower Bridge in London! Only small expedition and boutique cuise ships (58 meters with a shallow draft) can dock at "Tower Bridge Upper". If you are on one of these ships you will disembark right beside the HMS Belfast.