Most of the Soviet-era panel apartment blocks (https://en.wikipedia.org/wiki/Panel_building) have extremely shitty internal insulation, too. So you end up heating your neighbors, the street, the elevator shafts, stairwells etc.

You can't really fix that without extremely costly renovations.

Khrusschchyovkas (https://en.wikipedia.org/wiki/Khrushchyovka) are marginally better due to materials used, but they are 50 years past their demolition date by now, and will be also very expensive to retrofit.

There is also an insane number of new construction in the past 30 years. Perhaps for the in-EU Eastern European countries regulations and standards work. Everywhere else it's "whatever we build, as cheaply as possible"