Chen Xuefo has done many good things in ten years. Why did he die so miserably?

Learning Buddhism does not mean doing good. Doing good deeds is only a tiny part of learning Buddhism. These things are just like taking a postdoctoral exam, and not everyone who has studied Buddhism can understand them. Not everyone who learns can do it. Many many reasons. Even without reason, people will die. There is also that people who study Buddhism, like ordinary people, will be spicy if they eat Chili, and will die if they drink poison.