It doesn't seem logical to me. After all, Castro came out in favor of Obama. It seems like the least he could do would be to undo the embargo.
In seriousness, the US policy makers do not like Cuba because it represents what a country can do when a country begins to look out for its people instead of for big multi-national business. The US wants to embargo Cuba as a form of punishment and warning to other countries. The US has a long history of destabilizing governments that do not allow US businesses to exploit the country's resources and people.
An amazing fact is that when the US provides aid to a country with the aid of the World Bank, the countries GNP increases. After the aid is given, the population also experiences an increased level of starvation. It appears that US foreign aid mostly "aids" the banks and corporations involved in the projects to help the country. The projects involve US corporations with typically high capital cost that require greater national debt.
The US is being a total $$$$ for imposing an embargo on Cuba. There is no sound rationale except imperialism.