A perspective that must be understood is they do not want a total Russian collapse that would be worse. If Russia falls apart like a total defeat would cause then you'd have migrations and far more violence than now with infighting and likely warlords picking up Putin's remains and fighting for whatever is left.

They want a grinding war that ends up draining Russia so the people are sick of it and surrender not the government. Which is a much harder thing to do.

Blowing up Putin and the Kremlin is like blowing up a porta potty, shit everywhere. They'd rather it slowly melt away like snow.