Instead of writing what you don't know, maybe focus on what you do.
FWIW, I'm one of those people who's never taken a cruise (and so would not, ahem, presume to write about it) but my exposure to cruises has been as a longer-staying tourist on a number of islands, watching the rush of cruisers trying to experience a port city on a timetable. If you're familiar with any of the places cruises visit, maybe write about that. For me, the point was getting to know some of the local island people, appreciating the local cuisine (St Lucia's amazing for that - and also windsurfing if that's your thing). Bonaire for SCUBA (and hookah) diving. Diving's great off Cuelebra as well - and Cuelibra's part of Puerto Rico so no passport needed. Also, there's a bioluminescent bay on Vieques (also PR) which is pretty amazing to swim after dark, particularly if the moon is down (but I'm a distance swimmer). There are both pontoon boat and kayak tours. The people of St Kitts are incredibly welcoming and really nice beaches you can have to yourself or maybe one other party.
I'd go on about the Azores (another set of islands) but I haven't been there since the 90s.
The TL;DR of all this is that if you're an expat you're by definition living someplace most of the Medium readership is unfamilar with. Focus on that. See it through your "just got there" eyes. Write about that. What's cool? What's kind of a scam? What absolutely shouldn't be missed?
Just my $0.02 of course.