So after researching member nation of the current UN Security Council, I have a firm grasp on how a vote on UN peacekeeping operations would go.
This is an opinion based on information that is freely available. It is my opinion only but, using techniques I learned while on active duty it's probably not too far off the mark. This should answer the question, why hasn't this happened.
This post is not meant to assign blame, accuse an country of wrong doing or dismiss the severity of the situation...It is informative ONLY
Votes for Action: US, UK, France, Norway .. as members of NATO and with 'skin in the game' these nations would be a lock.
Most likely a yes: Ireland, and Albania. Both of these nations have had diplomatic ties to Russia in the last 40 years, however, relations have soured with both in the last 5 - 10 years with both countries condemning the recent invasion.
No votes: Russia, Kenya, Gabon, Ghana
Obviously Russia would condemn a UN peacekeeping action against them but the three African countries named have too much invested in Russia to 'bite the hand that feeds them'. Even though they have been mostly neutral in the General Assembly, their SecCoun votes would be enough to spoil a 2/3rds majority.
Possible no votes: UAE
UAE has been a strange mercurial player on the world stage. They don't want Islamic Jihadists or extremists ruling the Middle East (ie Iran) but also don't support Western openness characterized as Zionism. Russia has been very open to supporting their operations in defense of Iran without requesting more diplomatic openness to the Israeli state. While they most likely would abstain, there is a chance that they would vote no in order to garner diplomatic clout.
Abstention: China, India, Mexico, and Brazil
All four nations have very close diplomatic and economic ties with Russia, tourism is also very much a commodity among these nations. However, none of these nations currently have the want or need to support either side politically. This stance keeps them neutral on the world stage and allows them to supply whatever or both sides during a conflict.
Final Tally: 4(6) Yea 4(5) Nay 4(7) Abstain.
These numbers mean no direct UN action outside of General Assembly sanctions and finger wagging is incoming.
Now all this could change IF Russia pushes the nuclear option (UN GenAss'y could call for action with a vote overriding SecCon vote), Genocide becomes a major issue (GenAss'y could activate UNICEF and a UN peacekeeping guard with none SecCon membership - usually smaller nations that otherwise wouldn't participate, in this case most likely African nations that Russia has ties with in order to ensure Russia doesn't attack UNICEF ops) or the President of the GenAss'y could ask NATO to intervene, though at this point that seems unlikely.
Hopefully this answers all those questions without crossing any lines or inciting anger from outraged posters. (ie don't shoot the messenger).