Yeah, honestly even if someone catches on that someone was troubled they frequently wouldn't immediately jump to the parents being a factor. And socially, kids are taught to seek out an adult authority figure, so the idea that said authority could be part of the problem doesn't always come to mind for a lot of people.
It's especially the case with mothers because there tends to be a whole cultural thing with them, like "a mother's love is the only love that's unconditional," "your mother will always be on your side," "your mother gave you the gift of life and always does her best to support you through it," etc.
Which, naturally, are ideas bad faith actors more or less consciously take advantage of. An example in this story is the use of self punishment to control our protagonist while portraying herself as "the suffering mother who only wants to support you" to avoid negative repercussions for her behavior.
Kokoro may or may not have understood the dynamic if explained to her in very specific terms (which kids with abusive parents tend to not want to draw attention to the parents' flaws because ultimately this person still their parent), but lots of people will interpret this through the troubled child/suffering mother lens without very clear evidence to the contrary.
I would like to say adults should know better than Kokoro and have learned to recognize these patterns by the time they're older, but of course they often don't know better and that is part of why abusive parents can get away with a lot of stuff the people around them theoretically wouldn't be okay with yet end up abetting.