It's not due to US policy. Being a communist country, everything is owned by Cuba.
i am fairly certain you are wrong on this. Iran is another example of a country US firms are banned from doing business in. One US oil company was until recently doing maintenance work on an offshore facility owned by iran from a pre-revolution contract, but no one can do anything with iran proper. mark rich got into his bind over that, and had to pay off the clinton team to get a pardon much later.
look at all the european investment in foreign-tourist areas/hotels of cuba. there is a reason why no US company is there, and it isn't patriotism.