Because women hate each other. Many accusations of witchcraft came from other "witches" who were simply making petty claims against other women they disliked for any number of reasons. I actually have ancestors who were part of this where one women who was already named as a witch, and therefore going to be executed, just went balls to the walls at the end and took half a dozen other women with her by claiming they were also witches. This wasn't in the USA so no urgot poisoning as is thought to have been related to Salem.