You say this as if that is a voluntary, natural outcome for citizens in these countries... they grow up hearing their governments blame every problem (their gov created) on the west, while bad news coming out of the West is promoted widely to convince the public that capitalism is backwards.
So while I'm sure there are some intellectuals who are legitimate marxists in Cuba, I doubt the average working class person knows the difference. If they were given the option of the wealth of the average American (or even Mexican) or the cuban one I bet they'd chose the US in a second over the rampant poverty in Cuba.
The people in exile have seen what the alternatives are. They are better informed, it can't all be dismissed as bias. If anything they should have less bias than a Cuban who has never left that bubble.
And if you ever visit the non-tourist parts of Cuba it's incredibly depressing what socialism has done to them.