Or, a prolonged embargo, threats of invasion, actual attempts at invasion, diplomatic pressure to isolate, etc all by the most powerful empire in history on your doorstep destroyed everything.
It’s pretty hard to sort out after the fact.
That's just a longer way of saying socialism inevitably destroys everything it touches.
It is not hard, because you can look at other examples besides Cuba.
Once upon a time, there was COMECON, a huge bloc of socialist countries trading with one another, whose intent was precisely to limit Western pressures. It included some fairly developed countries like Czechoslovakia and GDR. 500 million people in total, similar to the US and Western Europe together back then. A huge market in total, from Leipzig to Vladivostok to Saigon (after it fell).
(BTW Cuba was a member of COMECON and it was a very non-productive member, being heavily subsidised by the Soviet Union all the time. I still remember the Cuban oranges sold in Czechoslovak shops, which were so full of stones/seeds that they were barely edible. No one would voluntarily buy them unless there was no alternative available, but there usually wasn't one. A good metafor for what was going on.)
They still ran their economies into the ground because Marxist-Leninist economy doesn't work in practice. Marxism as a theory is catnip for intellectuals, but neither Marx nor Lenin ever tried to run a corner shop, much less an actual factory. The resulting misalignment of interests throws off almost everybody and a country practicing Marxist-Leninist approaches to economy will end up with just two really functional institutions: the secret police, to keep the comrades in power, and the (very non-Marxist) black market, which is tolerated because otherwise the population would starve. If it is not tolerated, the population will starve, but only a few countries like North Korea were crazy enough to go down that road.
The same happened all over again pretty much everywhere where it has been tried. China only started to economically grow after ditching Marxist economy for market reforms in 1979. India was never totalitarian, but toyed with Marxist approaches until 1991, when the "License Raj" was reformed; since then, it has been following Chinese economic growth along a very similar line.
Heck, even very early idealistic Israel ran into somewhat similar problems, although all the kibbutzniks were there voluntarily and eschewed use of state violence to build their utopias.