I never got why buddhist monks set themselves on fire in protest.
Self-immolation is tolerated by some elements of Mahayana Buddhism and Hinduism, and it has been practiced for many centuries, especially in India, for various reasons, including Sati, political protest, devotion, and renouncement. Certain warrior cultures, such as in the Charans andRajputs, also practiced self-immolation.
Two well-known Jataka tales, Buddhist myths about previous incarnations of the Buddha, concern self-immolation. In the "Hungry Tigress" Jataka, Prince Sattva looked down from a cliff and saw a starving tigress that was going to eat her newborn cubs, and compassionately sacrificed his body in order to feed the tigers and spare their lives. In the "Sibi Jataka", King Sibi or Shibi was renowned for unselfishness, and the Hindu gods Sakra and Vishvakarman tested him by transforming into a hawk and a dove. The dove fell on the king's lap while trying to escape the hawk, and sought refuge. Rather than surrender the dove, Sibi offered his own flesh equivalent in weight to the dove, and the hawk agreed. They had rigged the balance scale, and King Sibi continued cutting off his flesh until half his body was gone, when the gods revealed themselves, restored his body, and blessed him.
The Buddhist god of healing, the "Medicine King" or "Medicine Buddha" (Bhaisajyaguru) was associated with auto-cremation. The Lotus Sutra describes the Medicine King drinking scented oils, wrapping his body in an oil-soaked cloth, and burning himself as an offering to the Buddha. His body flamed for 1,200 years, he was reincarnated, burned off his forearms for 72,000 years, which enabled many to achieve enlightenment, and his arms were miraculously restored.
Zarmanochegas was a monk of the Sramana tradition (possibly, but not necessarily a Buddhist) who, according to ancient historians such as Strabo and Dio Cassius, met Nicholas of Damascus in Antioch around 13 AD and burnt himself to death in Athens shortly thereafter.