Others have mentioned that many took one look and realised they'd be cannon fodder or third line guards and not ubermemschen driving tanks across the steppe and went straight home.

But also, the attack on the foriegn brigade training camp seems to have been far more damaging than admitted. One anarchist who came back disillusioned talked about many thousands of casualties from a few weeks attacks during training, and the rest deserted back home.

The death rates are also misleading since maiming is much more common with modern medicine. There was a recent article about AFU veteran in Chasiv Yar and he's lost a leg and a third of his company have some kind of permanent injury. New recruits tend to desert.

Now Russia has some similar issues, but it also has a lot more give.