Besides the specific limitations around Cuba, ITA Matrix only shows regularly scheduled flights generally available through airline Global Distribution Systems.
As such, it won’t show you flights on Southwest Airlines in the US (as they don’t publish their fares besides their own website). It also won’t show you more unusual flights, such as air taxi flights or airports only served by small airlines. For instance, you can fly out to Bathurst Island in Australia (BRT airport), but you won’t find that flight on ITA Matrix; it’s available through Fly Tiwi, an airline that offers flights to small communities in the Northern Territory on relatively small planes (under 20 seats). Countless similar examples exist throughout the world.
The Matrix does not show flights to points within Cuba.
This is because ITA takes a wide reading of the US Treasury regulations that forbid US citizens and companies from arranging or organizing travel to Cuba without authority of the Treasury. ITA’s exclusion of all Cuban points is probably wider than is really required but that is how they implement their legal obligations.
I have previously raised this topic with a developer at ITA Software. They foresee that US regulations will become more relaxed in the future and that there is no point in reconsidering their blanket exclusion at the moment.
Credit:stackoverflow.com‘