Why is AuthorDate displayed on git-blame?

Hey everybody, I wonder about the decision behind git-blame and git-annotate date that is being shown.

If I understand correctly, the AuthorDate is displayed, and I'd like to challenge that decision. Consider the following case:

A feature branch having commits authored last week, but merged to the main branch just today. And to the sake of discussion, let's say that the branch has a bug.

When someone encounters the bug on the main branch, he would probably want to know when it was introduced - the date when the bug started to affect him. However, git-blame only shows him when the bug was originally authored, in our case - *last-week*, which is confusing since the main branch was working just fine back then.

So I wonder why was AuthorDate the date chosen to be displayed under git-blame?