When South Park debuted, one of its most memorable and unique running gags was the recurring death of Kenny McCormick. The muffled-voiced, parka-wearing kid of the group died in every episode until his "permanent" death in Season 5. While the character has reappeared since, and still dies occasionally, the joke is no longer a staple of every episode. The reason why they stopped killing Kenny is quite simple: The show's creators got sick of the gag.
Source：https://www.cbr.com/why-south-park-doesnt-kill-kenny/
