Those leaving were 33 when the Soviet Union disintegrated, while those coming in were only 22. That means the former were fully formed by the Soviet system while the latter were only beginning their careers and thus have been formed primarily by the very different events of the 1990s and 2000s.
That doesn’t mean the new men in this case or any other are more liberal: they may in fact be deeply conservative and even more authoritarian than their predecessors. But their values are different, and their assumptions about their countries and relations between them and Moscow are different as well.
A great deal of attention in the post-Soviet space and the West has been devoted to questions about succession at the highest levels; but far less has been given to this generational change under the top, a shift that has been continuing and in some places intensifying even where the rulers remain in place.
Such attention is especially important now because over the next decade, almost all those who were formed in Soviet times will have reached retirement – anyone who was at least 30 in 1991 will be at least 69 in 2030, well past the retirement age for most.