One, social housing there is a very old concept, old and because of that, a significant portion of the population (>50%) lives in social housing, therefore because of how democracy works, they can vote themselves a great situation because they're the majority.

But if the amount of population in a city living in social housing is below 50% (most of Europe) then they don't have the democratic political leverage to vote themselves a better public housing situation, so social housing turns into a low quality charity for the poor and ends up turned into ghettos leading to a bad image of social housing leading to people to further voting even less in favor of social housing not wanting more ghettos.

Vienna, having the majority of it's citizens in social housing for a long time now has reached "escape velocity", that's why it works there but in no other EU cities who want to try it now, including in the rest of Austria where social housing is not the norm but more of a safety net for poor people and cities have even sold off a lot of their public housing to private investors in the 2008 crisis meaning replicating Vienna's success today would be impossible.

And secondly, unlike Zurich, Amsterdam, Berlin, etc., Vienna is not a tech hub, meaning it lacks international big wealthy companies with large offices of well paid workers from overseas, and neither is it a low-tax beach destination for wealthy digital nomads so there's not such a big pressure on the rental market from overseas workers with huge salaries pushing up rents and gentrifying everything.

That's the situation for rents. But the situation for buying a property flips on its head and makes Vienna one of the most expensive cities in Europe for buying your own property, far disconnected form average wages that almost nobody could afford to buy something.