What is the game desing philosophy behind imperfect parry having the same frame advantage of normal parry?

I might be late to the party, and this might be a discussed topic at this point. If this topic had a discussion before, please, submit the link and I will remove this post.

But that is it. I was just playing and realize it was +1 on imperfect parry/just parry and also +1 on normal parry. When I performed a perfect parry, it was +9. So it got me wondering, why not put some frames on imperfect parry too, just like the difference between Counter and Punish Counter?

Thanks for reading!!