In accordance with the minhag hamakom,I will attempt to answer my own question.
In a Chabad hagadah which has notes from the Rebbe and other Chabad rebbeim (could be the Rebbe's hagadah itself but not entirely sure), at the beginning of maggid it has a note explaining that (can't remember all of the names but I'm pretty sure) that the Rebbe rashab asked his father, the Rebbe maharash, why we don't say a brocho on maggid (for telling over yetzias mitzrayim specifically), and he replied that he didn't know
Then it says that the Rebbe maharash asked his father the tzemach tzedek, who also said he didn't know, who asked the mittler rebbe, who at first gave the answer of the Rashba, that it's already included in kiddush when we say "zaicher liyitsias mitzrayim", but that wasn't a fully satisfying answer since other brochos for mitzvos aren't simply included in other brochos in that way
Then it says that the mittler rebbe asked the Alter Rebbe who also said he didn't know
So how could I, or anyone else, possibly answer, if all of these torah giants, who know all commentaries and rishonim etc didn't know?
What's the one thing that all cases had in common?
They involved a son asking his father a question on pesach night, of why we do something differently
Perhaps this is itself the reason that the chochomim didn't institute the same kind of brocho for sipur yitsias mitzrayim: in order for the children to ask why this brocho is different than all other brochos