Book piracy is an old Russian movement to evade censorship, called samizdat, and these shadow libraries have their roots in that movement. It is an anti-soviet tradition, and probably has nothing to with wanting to cause economic harm to publishers.
Probably they wanted some royalty money. If I remember right, Western nations were sending some royalty money to Russian authors who had published their work in Western nations because it would have been illegal for them to publish in the USSR. Ironically, the USSR government then tried to collect these royalties.
Post-revolutionary Soviet state declared that private property was a sin, but life demanded immediate amendments that protected some rights for 5-25 years, depending on the content. That was inside the country, as international relations were broken.
As USSR turned into a “normal” corporate state with a twist, and began having economic relations with other “normal” Capitalist thugs, it started having minimal bilateral agreements that allowed things to move. Post-war reforms in local laws extended copyright terms inside the Soviet Bloc, and made them more similar to the Western agreements (even though licensing deals though the Iron Curtain were exceptions).
Finally, in 1973 USSR joined Universal Copyright Convention of 1952, at the latest possible moment its old terms were still in effect. As a result, everything published before 1973 could be used on old terms, — in particular, translations did not need explicit authorization. Of course, that hurt the Soviet writers in the same manner, but not a lot of people wanted to read Socialist Realist stories about imaginary workers of imaginary factories. As for everything published after 1973, All-Union Agency of Author's Rights handled and controlled all trans-border copyright transfers both ways, and dealt with the money — until the last years of Soviet Union, when free press, and private contracts with publishers made them irrelevant.
A translation of “Hobbit” was published in 1976, a print run of 100 000. An abridged version of “The Fellowship of the Ring” was published in 1982 and 1983, both runs of 100 000.
Even with the arbitrary government-defined ruble exchange rate, they probably wanted to collect at least some money.
Afterwards, post-Soviet countries joined the worldwide copyright agreements. One of the negative outcomes of those Soviet and post-Soviet copyright extensions made to align local and global law was that previously public ___domain content (like photos, which newspapers and archives often didn't even bother to track properly) became copyrighted once again, which usually put it into a limbo of orphan works, and prevented re-distribution of old products containing it.
