Lots of reasons, starting with the fact that US uses far more energy per capita than most countries. US also imposes its economic system upon the world that necessitates constant growth an consumption. US arguably being the wealthiest country in the word is also in a better position than most countries to actually do something about the problem.

Compare this with China which has an actual plan to transition off fossil fuels that it's actively implementing. China now leads the world in both nuclear and renewables by a huge margin, and continues to implement clean energy solutions at scale. If China is able to do this, then why is US isn't puling its weight?

Because among the countries that have greatly exceeded their fair share of CO~2~ emissions, the United States is the largest economy. Your link has some data relevant for future predictions and policy targets. However, when discussing climate reparations we must look elsewhere: cumulative CO~2~ emissions, technological and economic development, and vulnerability to climate change.

Europe and its settler colonies went on a global rampage for centuries. They built the largest human trafficking operation in human history, enslaving tens of millions of Africans. Wherever they went, they stole people's land, killed them when they fought back, and then took all of their resources as well. This still exists to this day, but in a less overt manner. It is why we have "developed" countries and "underdeveloped" countries. In reality, we mostly have exploited and exploiter countries. The loot from Africa, Asia, and the Americas kickstarted capitalism in Europe and the settler-colonies, and industrialization via fossil fuel extraction followed thereafter. The cumulative CO~2~ produced by these countries is not consistent with 1.5°C of warming, yet they expect the countries that they destroyed and left poor to do better while barely helping at all. To make matters worse, the exploiter countries continue to pollute, locking in more global warming. This will inevitably hurt equatorial regions more than themselves.

The US does have stacks of cash, and a decent industrial base as well. With a change of heart (lol), it could embark on a rapid renewable rollout as well as green, non-predatory international finance. Unfortunately, the only country doing something like this is China, which ironically has not wildly overshot its fair share nor engaged in colonialism. Still, China will probably exceed this fair share threshold. If the West was truly concerned about climate change, climate colonial reparations would have begun a couple of decades ago.

https://goodlife.leeds.ac.uk/atmospheric-appropriation/