Strict socialism tends to fail for damn near the same reason strict capitalism tends to fail, eventually what is formed is a wealth based aristocracy (you end up with oligarchical capitalism,) a government based aristocracy (you end up with tyranny,) or some horrible combination of the two where everyone else is in misery and poverty.
This is why just about every modern economic model is mixed.
The main problem with articles like that quoted by the OP is the silly assumption an economic model is either one or the other, where governance magically lines up behind the economic model desired and all things opposite end up as Venezuela.
It is easy to argue that Venezuela leaned left, leaned authoritarian, leaned socialism, and ultimately destroyed itself. But suggesting that socialism was the reason itself is bumper sticker thinking, what really happened is what I pointed out above. Aristocracy formed to the point that wealth held by the elites ended up held outside the nation away from the populace. What was being sold to the populace was only for them, those with power and influence arrived at a different conclusion.
What "always fails" is the accumulation of wealth and power by the few, and no matter if capitalism driven or socialism driven you end up at the same point of poverty for everyone else at the hands of very few holding the majority of wealth, resources, assets, what have you.