Because the West is guilty of far worse war crimes in the past 50 years, and the whole world knows this. To call Russia to the table for these wars, sets the precedent for other nations to do exactly the same for the USA, the UK, and their allies.[0]
Plus, there's that whole "nuclear annihilation" aspect to consider.
It's not capitulation. It is an attempt to attain peace and economic stability for the region in a way which will prevent the conflict from flaring up again in the near future.
Have you actually read the details of the peace plan, or are you going by media reports, exclusively? Be honest with yourself about this if you wish to discuss it further.
[0] I'm all for prosecution of Russian war crimes, if it leads to the exact same procedures being applied to the USA and its allies. The world is sick of war-monger nations getting away with mass murder.