It's difficult to discuss development in public places like here. There's always a hundred things on the backlog. People want this, other people want that and someone needs exactly the opposite if all of it. There are a a bazilion ways users can annoy each other and all of it needs fixing. Then a project needs to be stable and reliable. It also needs new features. Performance needs to be right... It's a proper nightmare job to balance all of it and maintain a mid-sized project. On top of it people will feel entitled, send in security vulnerabilities, complicated stuff that needs review and messes with things, other devs want something to be cleaned up, changed around, want someone to write more or less unit tests... and that also needs time for a plethora of good communication. And then there's the actual architecture design and coding, which isn't easy to begin with.

I didn't study the code. But I'd bet the representation in the database stays the same, no matter which way it's phrased on transport. It's some sql relation between answer and post either way. A UI will also want to know how to style a comment at the point it processes that comment, so it makes sense to have it there. On the other hand it makes more sense for the semantics to have it attached to the post. Then there's who can edit it. We need to trust incoming notes from third parties anyway. And maybe admins or mods can change it as well. They might be on arbitrary instances. So I'm not even sure if it changes anything with security.

And then there's always many ways to skin a cat in software development. We can have long meetings to write specifications. We can choose to be a bit more explorative and figure things out along the way. We can even choose to make mistakes and fix them later. I think that's a great thing with computer programming. Fixing mistakes is usually very cheap compared to for example a mechanical engineer who maybe likes to avoid wrecking a $1m piece of equipment. But that also means software developers have the opportunity to work a different way. And there's a time for each of the methods. The trick is to apply the correct one at the correct time. I really can't make a good statement here, I'd need to read the code and judge based on all the nuances I just mentioned. It's regularly not as simple as something appears from the outside.