There are several reasons for this:

1. the Russian leadership is nowhere near as aggressive and stupid as certain other states that are destroying their own country in permanent interventions.
2. Putin has never pointed out that it is about Russian geopolitical interests outside the Russian-held areas of Ukraine.
3. the primary concern in the Donbass is to secure coal and gas reserves. this has always been the strategic background to all the conflicts in the region
4. the persistent penetration by the propaganda media that Russia has an interest in invading other European states already makes the argument suspect
5. Russia could never hold a military position in a European state