The US doesn't impose secondary sanctions on Cuba, and a number of European countries have been doing a brisk business with Cuba for 50+ years now. In particular Spanish countries have a number of investments there. In other words, 75% of the world economy is perfectly free to trade with Cuba and has been since before Jimmy Carter was President. I don't really agree with all of America's Cuba policy, but there's a big difference between US-only sanctions and secondary (i.e. on other country) sanctions.

Also worth noting that US sanctions have a longtime exemption for American farmers to sell agricultural goods there