Russia does the same as the US did in Iraq and for the same reason. Russia uses old missiles as decoys for their real missiles to get Ukraine to waste anti-missile missiles.. In additiona, the dummy missiles get Ukraine to turn on anti-missile radar systems. Russia can then target and destroy the anti-missile systems.

I don't know who invented this tactic, but I do know that the US used it extensively in Iraq. The US (now Russia) got /gets to use up old ordinance that needed to be decommissioned anyway with some bonus results.