It’s a 10-minute edit window, not a 10-second edit window. 
Yes, the edit history is visible, but the effort of going back to look through a long discussion and adjust for all the edits can be pretty significant.
If one makes a mistake, a follow-up after the 10-minute window is up quoting the bit to be corrected with “here’s what I intended to say” doesn’t break the flow and makes it clear that it’s been edited, even for those unfamiliar with the platform.
Nobody’s expected to be perfect, so going back and editing a message from a day ago, a week ago, a month ago…Why? Just reply with the updated information, and then everyone knows what the updated information is.
Leaving the window short makes it easy for everyone, instead of assuming that everyone’s going to quote (not everyone does), and that when reading a quote from a message that was changed, they know to look at the edit history.
So, no, we’re not likely to change that.