One reason is the demographics.
1992 Russia population: 148,538,000
2022 Russia population: 146,325,000
Difference: -2,213,000
Russia births minus deaths 1992-2022: -16,310,000
Ok where did they get the 14.1 million difference?
Net immigration 1992-2022: +~11.6 million
Taking Crimea in 2014: +~2.5 million
Then since Feb-2022 and the war Russia has added probably ~8-10 million between taking the 4 SE provinces of Ukraine and getting millions of refugees from Ukraine.
The net immigrants Russia is getting for the last 20 years are young adult men and women from the Central Asian Muslim nations which are ex-Soviet Union countries. (also then those immigrants have been having children in Russia)
Lately Russia is talking about increasing immigration from India, Vietnam, China and African countries that are allied with Russia.