Attribution is the whole product
When somebody reshares your post to their story, Instagram renders it as a card: your image or video, your username as a sticker, and a tap target that leads to your post. It is a link with a face on it.
That is a materially different object from a like or a send. It is public, it is attached to another account, and it lasts twenty-four hours in a surface people check constantly. For the duration, your handle sits in a story run by an account that is not you.
The value follows from that. Reposts are worth ordering when the goal is your handle attached to a reshare rather than inflation of a number — not a promise that anyone on the other side sees it — and they are the wrong tool when you simply want a post to look more popular, because the repost count itself is not what visitors see.