Occasional wet floors due to condensation, flooding? Just guessing.
I read commentary earlier this morning that said it was because the walls are/were so thin that rugs were hug to try and soundproof the rooms (I’m guessing it helps with temp control, too). It may have become habit or a part of culture now?
Rugs on the wall are a Russian hillbilly thing. The majority of Russians are laughing at it too. Not to mention that the majority of pics are from Abkhazia - a Georgian breakaway region. I’ve been to Sochi some 15 years ago and it was pretty lavish at the time. Sure, they have ghettos too if you are to look harder but I think most of it were redeveloped over these years.