I'm surprised too but my take is this:
China got a very high score because China had the perfect conditions for this to have become a disaster of epic proportions. Massive population, massive population density, during flu season, coinciding with the migration of Chinese New Year, and it is the only country to have no warning before COVID-19 struck. But, under CCP managements, only 4,600 people died, and then compared with American and European death tolls, Chinese citizens are truly appreciative of how well-protected they were. The contrast between everyone expecting China to do worse than the developed countries in healthcare and seeing what actually happened was an incredibly delightful surprise that probably spurred top marks for the CCP.
Japanese and Koreans tend to be more on the negative/pessimistic side in general about their government and lives. People complain all the time that they are worked to the bone for little pay living in cramped cities, always showing displeasure that the government cannot change this. They have high suicide rates to reflect this and thus, anything the government does that is less than perfect will be seen with great scorn. I think it's undeserved, as these governments are doing a fantastic job in lowering death toll compared to the US and EU despite closer proximity to Wuhan, but these countries are full of people who are unhappy and like to complain.
Low scores and among prominent European countries with high death tolls and the US: well deserved, no explanation necessary. Scores were too high if anything, especially for the US being a third wave country that liked to tout its medical supremacy to the world. Undoubtedly the number was greatly inflated by ignorant people who still think the pandemic is a joke and the POTUS can do no wrong.
