It didn’t last because the will of bureaucracy was placed before the will of the people, it was a long decline of democratic rights of the working class started under Stalin and continued by all following leaders. It was not due to socialism per se, more due to the specifics of CPSU politics. China seems to have figured out a better way to do democratic dictatorship of proletariat and is successfully combining aspects of capitalism and socialism, to both make the country appealing to capitalist investors and also build up a socialist economy to bring the living standards up. It’s not perfect (and is definitely not “the end of history” by any means), but it is doing fine as an interim solution.