That’s in part because they are far past their original designed lifespan, as these were meant to give everyone a house. Despite their other egregious excesses, the Soviets at least said they believed in housing as a human right, and implemented policies to that effect. Not only for building housing at record rates with innovative prefab construction, but also for upkeep of those buildings.

That is in stark contrast to the radical chicago school of economics “reforms” after the collapse of the soviet union, which basically created an oligarchy overnight. Those buildings were sold for pennies at private auctions to private landlords. Whole populations who used to have the security of free public housing, suddenly found themselves having to rent the house they have always lived in. Meanwhile those landlords never have nor will invest anything in upkeep, which likely accelerated the deterioration of these buildings significantly.

I do agree social housing should if possible be beautiful. However, the first concern should always be to build enough of it so everyone who wants housing can get it. Most of the western world is in a deep housing crisis, so IMO any social housing is beautiful.