Why wouldn't Haiti or the Congo be better off if they became socialist?

Say what you want about Cuba or the USSR's standard of living compared to the USA but there is no doubt whatsoever that it was better than these hellholes. Thanks to socialism the USSR went from being a miserable backwater decades behind the rest of Europe to being one of the pre-eminent military and industrial powers in a rapid span of time, lowering homelessness and poverty, raising literacy and life expectancy. No, it wasn't a paradise compared to America but compared to Imperial Russia (and arguably modern Russia) it was much better.