Why is it so rare that main characters in anime actually have parents? Or if they do have parents, they’re away on an extended trip, or just never show up in-show. Given how unlikely it is any teenager would be left to their own devices in real life, it seems weird that this comes up so often in anime.
This isn’t actually something that’s specific to anime – if you look at young adult literature in general, or western shows aimed at teens, you’ll see a whole lot of absent parents. And there’s solid, specific reasons for that.
First, parents kinda dampen the storytelling common to these works. Most stories with high school-age characters just don’t benefit from parents – they’re adventures, they’re romances, they’re all based in the sorts of things kids do when parents aren’t around. They’re escapism, basically, and parents ground this stuff, and draw focus away from what these stories are intended to be about. You can’t have five girls suddenly crowding your house if your parents around – you can’t spend a week away in search of the Demon’s Skull if your parents will call if you’re home late from school. Second, removing parents also gives kids no higher authority to turn to – it increases tension when the protagonists have no-one to rely on. And finally, many of these stories actually start as the kids break from their parents – because of that, their entire world has a fresh slate, and so you can essentially ride along with the character as they enter the stage their story is depicting. This is somewhat related to why sports or fantasy stories so often center on “the rookie,” an outsider in their world – not only does this facilitate a classic hero’s journey, but it also both allows the viewer to better align themselves with the protagonist (since the viewer’s reactions should be similar), and allows the story to dabble in exposition that seems natural (since while explaining the rules of a sport directly to the audience isn’t graceful, explaining it to the rookie audience proxy is absolutely natural).
Kinda continuing from that set of points, it’s also a generally accepted truism that every element of a story should be critical to that story. Not only does adding parents add a set of relationships and baggage to explain to the audience (something which also distances the viewer from the protagonist, since the viewer necessarily doesn’t have that connection with the parents, whereas the viewer will ostensibly have “standard” reactions to whatever new characters the show introduces), but if you have parents in a story (and you’re trying to write a good story), you kind of have to make use of them. Which is why often high-school stories with actual parents tend to be family stories – shows like Clannad or Toradora feature parents because the relationship between parent and child is actually a critical part of those show’s goals. But if your show doesn’t have family themes, then adding scenes with the family often just draws focus away from the characters and relationships that are actually central to your show. Meaning parents/siblings either get a couple scenes just to establish a home life/context for a character, or are absent entirely.
So while it’s kind of weird to think of stories in general as existing in a world where parents are an exotic rarity, on an individual level it often makes a lot of sense to leave them out.