What appears to be the principal driver for the disappearance of Coelodonta antiquitatis around 10,000 years ago?

Climate change leading to the replacement of the grassy steppe ecosystem.

The ultimate decline and extinction of the Woolly Rhino is most strongly correlated with fundamental shifts in global climate occurring at the transition from the Pleistocene to the Holocene epoch, specifically following the end of the Younger Dryas period. As the massive continental ice sheets retreated, global temperatures rose, fundamentally restructuring the environment. The specialized ecosystem that supported the Woolly Rhino—the cold, dry, highly productive mammoth steppe dominated by grasses and sedges—began to break down. It was replaced by moister, shadier environments such as forests and denser tundra. Since the rhino was highly dependent on the specific forage provided by the steppe, this habitat loss effectively removed its primary food source across its range. While human interaction may have acted as a compounding final stressor in certain regions, the primary, large-scale cause was the pervasive restructuring of its required biome.