I looked into this issue a while back. I think the reason is that many forum software packages have to feature to only allow edits to a post made for a short period of time. This may have been the result of spammers who post a perfectly legitimate post, only to come back after it falls off page one of the forum to post spam, illegal content, etc.

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Timed 2:53 PM EDST Tuesday, October 13, 2020
David_NYC