Unless someone can come up with a good argument for the first of these, I will dispense with the issue of money paid. Although this is much more than what they would get in their civilian lives, it does not seem sufficient for such a sacrifice. Of course mercenaries from China and Africa are appearing in the Russian ranks, but they probably have no idea what is happening on the frontline. Surprisingly, Africans going there are hoping for Russian nationality as well as pay, but in the present Russia looks like a sinking ship, slowly submerging, although that could change.
Propaganda is the answer as from all the evidence Russian men believe it, not just the poorly educated. Russian propaganda functions like wallpaper, created from vivid colours but otherwise blending into Russian lives. Not just Russian. I often hear Americans, especially Trump followers, repeating it without realising the origins.
The propaganda aligns the war with WW2, the fight against the Germans, perceiving NATO in the mode of a joke factory as the new Nazi. Killing and torture of Ukrainian civilians is done to discover Nazi amongst the population. Russia, no matter its crimes, is seen by Russia as morally superior and do not recognise their role as expendable puppets.
Any explanations you can offer?