I messaged an admin before about this and they told me it's to prevent spam. Some spambots are getting smarter. They post a regular post to bypass the spam filter, then later they edit the post to include a spam link.
I have had issues where I wanted to go back and edit stuff but I understand not allowing it due to spam. There are spam accounts that are run by people who know how to get around these things now. If it is an option, maybe having a "request an edit" would be helpful. You make the edit but it has to be manually approved by the admin or mod.
Spammers ruin forums for members. I have dealt with it myself. I was a moderator on a forum for almost 6 years and the spam was just annoying. We kept having to use new plug-ins to counteract it and eventually removed the option to edit posts for people that had fewer than 50 posts on the forum.
