Why can`t I take American Express travelers cheques to Cuba or use U.S. cash in Cuba?

Because there is a trade embargo between USA and Cuba..

You can but you will be charged a penalty for changing them. About three years ago Castro decided hedidn't want them. You can check the site below for more info and Oanda.com for conversion rates of CUC (convertible pesos.

some places just don't accept american money and that's their right to decide what kind of money you can use there. surely they at least have exchange services? anyhow, be safe and make sure you get some pesos before you go!

Credit Cards and Travelers Checks issued by U.S. Banks cannot be used in Cuba because of U.S. Laws against Trade with Cuba. You can take U.S. currency and exchange at any currency exchange, banks and most hotels (avoid exchanging at hotels as this is a ripoff). Check the U.S. State Department website as well as the Cuban Bank websites for current exchange rates. The Cubans charge an additional 10% fee to exchange USD to CUC (the Cuban Tourist Currency).

because americans are not allowed to visit cuba

Because the US government will not allow US financial institutions to have dealings with Cuba. You can exchange your US funds there but you will be charged at least 10%. So it´s not worth it for you to do that.

Because they don't accept it and charge a huge fee to change it into CUC - You do know that relations aint good between the US and Cuba.

because cuba does not like americans and US has a trade embargo with cuba. im from the virgin islands and i speak cruzan thats how i save my *** when in cuba.