There is a very compelling reason for that. If you don't understand why, I could explain it to you.
Basically, if we allow editing, then credibility is thrown out the window.
Right now it is just like being somewhere in person. If you say something to others in public, you cannot unsay it. So be careful what and how you say things. Unlike being in public, you have time to edit what you type for as long as it takes for you to provide constructive logical responses in a forum maintaining respect for everyone else (and yourself).
Not everyone does so, but we are dealing with humans and they (we) are not perfect.
You have all the time in the world to edit your comment BEFORE you hit the post button. So it does allow 'editing' and it is your responsibility to ENSURE that what you have typed in is proper before hitting POST.
In your case of having previously posted reference to information that is wrong, there is nothing wrong with admitting it was wrong and publicly saying so here. I think you will find that you get more respect for admitting mistakes than for trying to hide them.
I’d like some kind of, maybe notice above the post ‘this was wrong’ by the user or a moderator. Leading the post as-is, when it needs to be modified or retracted in a new forum is a fatal flaw. Keep links to the original.
It’s not that hard to implement those things.