It's because the USSR called themselves a socialist state, born out of revolution and meant to be a stepping stone to communism. Since Marxist communism as they envisioned it (classless and stateless) is an impossible utopia, they were stuck in the socialist phase forever. Of course the socialist state made it pretty cozy for those in charge, so I doubt they were in any hurry to really try to move on either after the initial idealistic fervor had died down.I am sorry, I have three questions:
- why is so often this idea that "everything else" has to be socialist?
- why so often "socialism" = Stalinist/Maoist like state?
- why so often we believe socialism => repression?
Western Europe have never been socialist, it's social democracy which is not the same thing.
Socialism is about the public (mainly the oppressed masses, the working class) in one way or another owning the means of production, which means they have to first take control of the means of production. The state, representing the working class, then takes control of economic activity as a whole - socializing it. Back in the early 20th century, the states were obviously not going to do this, so the states had to be replaced first by revolution and the means of production taken over by violence if they were not handed over "peacefully". Then to keep the whole thing together and to brainwash the populace into the new way of thinking needed to abolish the state and implement real communism, a constant repression of "dissidents" (normal people who resisted the brainwashing) was required.
In the social democracies the replacement of any states were definitely off the table. The societies were to be improved though democratic means and within the existing state's own rules. Socialization of the means of production was not necessary to achieve social justice. So under the social democracies, the state created state-controlled institutions to promote social justice. Everyone, regardless of class, was to get access to and be able to afford good education, good healthcare, the same access to emergency services, the same access to postal services etc. No-one needed to go hungry. But the economic system outside of what was needed to deliver this could stay private and capitalistic. This was to be paid for by taxation and since well-off people could afford it anyway, progressive income taxation was an important tool to even out (but not eradicate) economic and social inequalities. You could live a comfortable and respectable life regardless of your class, which was seen as fair and just since all the classes were needed to keep society going anyway.
The entire basis for socialism and social democracies are completely different, even if they both tried to right the same wrongs in the end (the oppression of the many by the few). This is also why the socialist states hated social democrats - they were living proof that the same ultimate goals could be achieved another way. Revolution had not been necessary after all which undermined the legitimacy of states like the USSR.
In the USA and also elsewhere sometimes it's popular to equate the two in political rhetoric. Either the people doing this are deliberately lying for populistic reasons or they have no clue about the subject.