I’ve definitely thought about it, probably have written somewhere about it. I’m not really sure why it happens but it’s definitely very common to kill off the mothers in children’s stories (or sometimes the dad). I remember when I was little thinking it was really weird that Mary Kate and Ashley were always missing a parent in every single show or movie they starred in even though they always played different characters.
I think part of it is that it’s a really easy sympathy thing, IMO it’s kind of a lazy shortcut to creating empathy for a character. Everyone will feel bad for the kid without a parent, and it just becomes one of those common tropes in film/stories.
On the other hand it could be an expression of some subconscious ideas about women/mothers… not necessarily that we have to kill them of course… but more like… them being absent, even though it often creates problems for the protagonist, prevents anyone from having to develop them as a character. They’re just a generic “mom” whose imagined role only has to do with raising the protagonist and being there for them.
So I think that bothers me a lot. Mom characters are often stereotyped and troped when they’re in movies and seen as appendages to their families rather than as individuals with their own stories to tell, and when they’re cut out of the movie completely they become even more generic and just like a metaphor for “something child is missing.” They’re never imagined by the child as being real people- they’re always imagined as incredibly idealized and only doing mom-role things.