Because it's not as easy anymore to just grab all the central Asian and/or Caucasian recruits to do their dirty work. They need to recruit from actual Russian-Russians, and those boys can't fight for .
Now some of the Central Asian republics are pushing back:
https://www.rferl.org/a/russia-uzbek.../31981901.htmlIn a statement issued on August 10, the Embassy of Uzbekistan in the Russian Federation said any form of participation in military activities on the territory of foreign countries is considered to be mercenary activity and will be punished by up to 10 years in prison.