Final answer:
Allah (swt) sent severe punishment to the people of Thamud because they rejected the prophet's message, worshipped idols, and harmed the she-camel.
Step-by-step explanation:
Allah (swt) sent severe punishment to the people of Thamud primarily because they rejected the message of the prophet sent to them, worshipped idols and abandoned monotheism, and harmed the she-camel, which was a sign from Allah. These actions were considered grave sins in Islam. The people of Thamud were given ample warning and signs, but they chose to ignore them and continue their wrongdoings, which ultimately led to their punishment.