Because they stopped being communist.
>The Soviet government was democratically elected by regional worker organzationshttps://youtu.be/9PoYzPfguJc>CIA documents show that the gulag system killed about 5 million people from 1917 to 1954, more than half of which during ww2 (i.e nazis and fascists).https://www.cia.gov/library/readingroom/docs/CIA-RDP80T00246A032000400001-1.pdfhttps://www.cia.gov/library/readingroom/docs/DOC_0000500615.pdf>2 CIA documents talk about how food consumption in the USSR were on par and at times even more then the U.S.https://www.cia.gov/library/readingroom/docs/CIA-RDP84B00274R000300150009-5.pdfhttps://www.cia.gov/library/readingroom/docs/DOC_0000498133.pdf>Russians have less food now than at the end of soviet timeseuromaidanpress.com/2017/02/06/russians-consume-700-calories-a-day-fewer-now-than-at-the-end-of-soviet-times/>Study comparing living standards, leisure, and development of socialist and non-socialist countries in the 20th centuryhttps://ajph.aphapublications.org/doi/pdf/10.2105/AJPH.76.6.661>The USSR had relatively low taxeshttp://www.garant.ru/files/1/3/621831/chast2-01.jpg>In the USSR, Russia had a much lower crime rate and incarceration ratewikipedia.org/wiki/Crime_in_Russia#/media/File:Crime_and_incarceration_rates_in_Russia.svg>The USSR created the first satellite and space station, put the first man in space, created the first spacecraft landing on the moon, the first landing on mars and on Venushttps://en.wikipedia.org/wiki/Soviet_space_program 