Analysis / Death by Childbirth
It seems as though, in a certain subset of cases, this trope is applied to the mothers of violent anti-heroes or villains to show that yes, there actually is something "off" about these characters going back at least as far as their birth (picture Voldemort from Harry Potter). There may be a couple of reasons why this works: it subtly makes the case that the character is so steeped in death and suffering he couldn't even help but kill his own mother, and on the other hand, his mother's death might be the one death related to him that he did not willingly cause (and indeed might have contributed to his going evil if he later suffered abuse or neglect from whoever his parental figures were). This trope is also quite popular with fangirls: quite a lot of fangirl-pleasing characters have it in their backstory and if it's not there, a fangirl may add it later. One possible example of this phenomenon may have occurred in the Pokémon Black and White fandom when N first became popular: the idea that N's mother died in childbirth, despite never receiving any confirmation from canon, has since been found on This Very Wiki, in at least one Tumblr headcanon post, and in no fewer than two fanfics!