The Russians/Soviets saw that the end of the line was near as the empire was collapsing into bankruptcy. They lacked the money, economic might, technology and market to even break even and needed a lot of the former to stay alive. Thus they reverted to use the one key strategic thing that had always saved them, i.e. give up some lands for time.
They did it to Napoleon and then Hitler, and now they are doing it again. When they feel strong enough again they set about to reclaim the lands they retreated from earlier. This is exactly what we are witnessing with Putin.
I would not disagree, however, this was a large-scale withdrawal with no guarantee of a successor government that would want to return, and we have options of making friends with the liberated and helping them maintain their freedom, most of which options we have taken. Even the Central Asian republics are probably in a better place now than under the Moscow rule, perhaps not all. The Baltics and Ukraine and the Caucasian republics have all done okay but some are getting push back. Moldova and Belarus seem more interested in playing along with Moscow to some extent.
The world is somewhat safer with the actual communists gone and the quasi-communists in charge in Moscow, and there will be a few years yet before they try to reclaim much more of the lost territory. Our task should be to befriend the most liberal-democratic groups in Russia to bring them closer to power after Putin’s gone. Perhaps with them in charge, the losses would be permanent and to some extent unlamented. Russia’s a pretty big country even without the other fourteen Soviet republics (the U.S.S.R. was about the size of Canada plus the U.S.A., Russia was three-quarters of that).