Incredibly low compared to whom? The US that had a couple hundred years of head start from exploiting black slaves (where do you think all the wealth in the American South came from) and looting resources from overseas colonies?

The fact that the USSR was able to close the gap in such a short period of time was exactly the reason of widespread anti-communist propaganda, the meddling of political affairs in post-war Europe including arming fascists through Gladio to destroy the European left, and ironically, financial aid to rebuild Western Europe because they were really afraid of workers uprisings bringing post-war Europe towards the Soviet sphere.