Most likely russia calculated that surviving 1st liners would reinforce the 2nd line and the more elite reserve troops would counter attack when possible.
Lots of running away dropping weapons instead of organized controlled retreats russians are now known to be able to do. Maybe the competent commanders are really purged again.
That 60/20/20 split for the three main defensive lines was an Ukrainian military assessment when the offensive began…
Most likely russia calculated that surviving 1st liners would reinforce the 2nd line and the more elite reserve troops would counter attack when possible.
Lots of running away dropping weapons instead of organized controlled retreats russians are now known to be able to do. Maybe the competent commanders are really purged again.