I’m sure this is related to the fact that the editing window closes here after a short time.

I’ve been on other forums where disgruntled users have come through and destroyed old posts, which resulted not just in the loss of the messages but also harms the thread that built upon the now vanished post. So they, too, have a short editing window policy instituted.

Yes I'm sure companies can think up a whole array of excuses as to why they won't delete your data :)