You can’t serve in the Russian military with the history of conviction.
The shortage of manpower in field is the result of expanded goals.
The original was the liberation of Donbas and Lugansk which Ukraine rejected, meaning it is now the war to the end.
The existing force is enough to kick butt, but not enough to hold gains as evident by Harkov situation.
You can’t remove forces elsewhere because other threat may emerge.
How could you incorporate militia before their states entered the union?
“Expanded goals”?
Every regular unit in the Russian Army has already been identified in Ukraine. They have even drawn garrison units from every border, including those assigned to, say, hold down Dagestan or watch the Georgian border.
If your army cant hold ground it cant “kick butt”, because it cant attack in any significant way. It leaves the enemy with the initiative, and the ability to, say, cut your supply lines, as the Ukrainians did. As in cutting the main railroad route into Luhansk/Donets (from Belgorod, the MSR), and putting the other under fire. There is only the line from Crimea fully functional, and its trucks from there.
As for the rest, excuses. Bureaucratic bumpf.
Re prisons - Yeah, and the workaround of course is to set up a PMC to do that recruiting in prisons, so you can actually do it.
Manpower shortage.