Some of these mods add in a supernatural aspect.
Another reason to have this type of mod can be for acting out your favorite scenes from movies or making your own type of movie. Violence and killing are sadly a part of our waking world. Why would someone want to have these sorts of mods? Sims 4 isn't very realistic, and a lot of simmers crave to have realism in their game, which includes violence. Kill mods, as the name would suggest, involves killing sims. While these mods serve as an extension, they are not for the faint of heart.
Killing mods bring a more realistic approach to Sims 4. It's no secret that death is a part of the Sims 4, and sometimes you want to have more substance to it.