Sint Maartin, Aruba and Curacao are not sovereign nations. If they are to be included, why not include Martinique, and Guadeloupe, Turks and Caicos, Dominica and all the island in the Caribbean for that matter.
To comment on your specific localities: Dominica is too far away. Martinique and Guadeloupe are parts of France. Turks and Caicos are a British Overseas Territory (I suggest you check on what a BOT is, but suffice to say here that it's not a country).
On the other hand Sint Maarten, Aruba and Curaçao are all countries (not territories, or parts of other countries), which is why they appear here. This quiz makes no claim about "sovereign" or, well, "non-sovereign" countries, so the use of that word in your comment isn't relevant here. We will point out, though, that all three of Aruba, Sint Maarten and Curaçao have a sovereign, namely King Willem-Alexander. The country of the Netherlands, and these three countries, comprise the Kingdom of the Netherlands.
To comment on your specific localities: Dominica is too far away. Martinique and Guadeloupe are parts of France. Turks and Caicos are a British Overseas Territory (I suggest you check on what a BOT is, but suffice to say here that it's not a country).
On the other hand Sint Maarten, Aruba and Curaçao are all countries (not territories, or parts of other countries), which is why they appear here. This quiz makes no claim about "sovereign" or, well, "non-sovereign" countries, so the use of that word in your comment isn't relevant here. We will point out, though, that all three of Aruba, Sint Maarten and Curaçao have a sovereign, namely King Willem-Alexander. The country of the Netherlands, and these three countries, comprise the Kingdom of the Netherlands.