Or you could say that post-1991 they had other things to do (to survive, or to entertain themselves: Western movies etc became available.)

However I was thinking already 1980's: probably the dysfunction of the economy had an impact on people people's reading (like, do you typically read a book while you are at the meat shop queue or shoe shop queue?)

After 1991 they have a lot of other entertainments to spend a time on - pirated videos, more than 3 state-approved TV channels, spread of BBS, FIDO and Internet...