I respect your service. How willing would any army be to fight for a system that oppresses them and views their lives as so much cannon fodder?
Same reason the Kims are still in charge in North Korea: They don’t know any better.
You need to read some Russian history. Its very depressing (just like Russian literature...).
Russians and other former subjects for the Russian Empire were not treated any differently by the Soviets than they were by any Russian government before them. Some of them might have actually been treated somewhat better.
Add to that, the natural paranoia of a country that has been repeatedly invaded (including by us) and taken millions (yes, MILLIONS) of casualties, and, well, it makes sense.