Stupid answer. Most sites time limit is getting into the post. Then allowing the person to accurately fix the post. This site has the shortest time limit. Thus instead of fixing the post additional posts are required!! Thus adding confusion.
some sites allow editing without limit; you could go change what you said 8 years ago.
suppose you were arguing with someone, and they say, 'but you said _____' - and they were right, _____ was wrong for you to say. a dishonest person could go change what they said, and then say, 'no i didn't, go check the post'
i believe that's partly what a short edit window is meant to curtail. because if someone goes back later and reads through a thread that's been edited after other replies are posted, it can become confusing, with people replying to things that no longer exist.
the other thing, is that it encourages us to think about what we're writing before we press the 'post' button, instead of afterwards
i know this 5-min-rule has bothered you for a long time, but i really don't think the site admins are ever going to change it.
whatever case you plead, the answer is going to be, proofread your replies before you post them.