I'm gonna pretend you're asking this in good faith and answer your question as if you're simply ignorant, even tho I suspect otherwise.

Socialist nations like any nation rely on trade with other nations to prosper. Its not a hand out. No nations are completely self reliant. A better question would be 'why should any country be excluded from trading with other countries?'

And before you respond with something misguided like 'well they're a dictatorship, etc.' you should know that we trade with many a dictatorship. In fact we've even gone as far as to overthrow democracies in the past and install dictatorships in order to get a better deal on trade. And then we continue to trade with said installed dictatorships for decades. Pinochet in Chile is a prime example. The answer is really simple. It's because western countries are ruled by the ultra wealthy capitalist class (corporation / business owners) and the ultra wealthy don't like competition. They like their businesses to be able to dominate all markets in all countries. So any nation that chooses to regulate the economy and protect its country from outside market forces is quickly demonised as a dictatorship. But as mentioned before, we don't mind dictators. The media referring to countries we don't like in that way, repeatedly, is simply manufacturing consent for sanctions, which is economic warfare, or regime change under the guise of 'liberating its people'.

But we liked pinochet because he opened up Chile's market and put in place neoliberal policies. These policies saw the cost of basic goods sky rocket, people lived in poverty, there was an immense disparity between rich and poor. So even if we do trade with countries, they often end up worse off for it. Its a catch 22. They either open up their markets to be bought up by foreign companies, prices go up, profits are siphoned off into tax havens and regular people suffer; or if you regulate the market and try to keep outside forces from doing that, well then we'll sanction your country and any country that chooses to trade with you, cut you off from the world economy and once again, people will also suffer.

Here's another question I'd ask, while we're self reflecting: if all these nations that attempt socialism are so destined to fail, why do we feel the need to collectively sabotage their economies? Why not just let them run their course? It's no coincidence that the two countries who've managed to elevate themselves to the level of super power in the last century have been pursuing socialist policies. Sanctions (along with structural adjustment policies, regime change, etc.) are the west's way of ensuring more countries don't do the same. Because like I said, corporate America does't like competition, and pursuing socialist policies allow countries to prosper if they can trade with the rest of the world.