Articles for countries

In one of the answers to a question in the corresponding lesson regarding articles for countries, Cécile advises that Israel and some random island countries like Malta, Cyprus, Haiti and Cuba do NOT take an article (le, la, les or l’). From the above exercise it appears that Monaco is also included on this small list of countries without a gender. Just out of interest, does anyone know why Monaco doesn’t have one? I wondered if it was because it’s just an abbreviation of la Principauté de Monaco? (But then again, the names of most countries are abbreviations of their official names, so that doesn’t help us to decide whether to add an article, and maybe it’s just something we have to learn individually for each country)