Families of people who signed up for the war got large amounts of money. The transfer of money from the Russian national wealth fund into the economy, together with the shortage of workers, increased salaries.

[Edit] People didn't keep that money but spent it so others profited from that money too.

This is what happens in wars - beside war racketeers - salaries go up. There is a lot of research on how German profited from WW2 (and before) for example for most of the war. WW2 too seems most researched from what I see on how everyone profits until things get worse and end.