Well, let’s put it this way.
New Model Army
A few days ago, Russian state TV reported North Korea was ready to send 100,000 soldiers to help Russians in Ukraine. Now, this isn’t something entirely outlandish, North Korean workers are already present in Russia. They’re treated as employees of the North Korean state and their wages are paid directly to North Korean government, who then compensates the workers (or rather, pretends to). There is a framework in place that would enable Russia to actually hire 100,000 condottieri for dirty work in Ukraine. It also happened before, albeit not at this scale – in 1982, a North Korean brigade was brought in to quell unrest in Zimbabwe. It was rather brutal, as you might expect.
So, how does this relate to the question? According to Pentagon, their intelligence has proven spot on thus far, Russia already lost about 80,000 men in Ukraine. They are not able to replace 80,000 men and are instead looking to hire North Korean grunts at exorbiant prices instead.
If you aren’t able to replace 80,000 casualties you sure as hell don’t have the ability to mobilize 10,000,000 men. I don’t know why that is, but you don’t, period.