Probably because that's how Gypsy Rose Blanchard killed her mom as revenge for the brutal Munchausen by proxy she inflicted on her (
Wikipedia link).
As a true crime genre addict (I know, cringe), criminal profiles describe the choice of stabbing as a distinct method that is overwhelmingly likely to indicate:
-personal relationship between victim and offender, or criminal feels very personally slighted by the victim (it requires you to get up in the victims face, and repeat the action and not stop, and watch them die, and see them watching you kill them)
-oftentimes sexual in nature by its association with penetration and destruction of the body, a kind of proxy for rape or sexual mutilation
Notable examples include Ed Kemper's early attacks (before he abandoned it because it 'took too long' and 'its not like the movies- you have keep doing it over and over until they leak to death): he felt personally slighted by the college girl victims who he felt as a cohort rejected him sexually
-Lizzie Borden (hatchet but no one owns a hatchet as a household object anymore, knives are more common)
... Other examples that I can't remember because I'm very very tired. But it's a strong clue for criminal profilers looking at a scene- personal, and sexual in nature. Similar to a killer covering up a body after death- indicates they had a personal relationship with the victim.