You could make a lot of deep theoretical points about it, but for me its very simple. Cuba is poor and poverty is shameful for libs and many baby leftists, therefore Cuba is invalid and bad.

They want a world where people can be rich, they don't want to be seen as embracing poverty. Supporting Cuba means "supporting" poverty. It goes against their entire world view.

Scandinavia is rich, therefore there is no shame in supporting them even when some of their values goes straight up against American values.