When you restrict it to fit men of military age (lets be generous here and say 18-55 , even though there is ample evidence of Russian men 60+ signing up), 1 million is quite alot. The Russian population skews older - median age is around 40. There is also a massive gap of of people their 20s-early 30s.

1 million is basically an entire birth year of men ages 30-45, or two entire birth years of their male population from ages 20-30, https://en.wikipedia.org/wiki/Demographics_of_Russia#/media/...

Imagine all the men of your entire high school / college graduating class being either killed or seriously wounded so Putin can grab a few thousand km of territory.

Now they could allow women in combat roles, but I severely doubt it for this conflict. It would be extraordinarily unpopular and go against the narrative they have been selling their populace for decades.