Why are titles and replies on the main site only editable for five minutes?

My Boards replies can be edited whenever I like, but titles and replies on the main site and sites like Nexus only allow me to edit them for five minutes. I'm fine with the title lock, just I feel like five minutes is a bit short. As for replies on the main site, I don't understand why there is a lock on editing at all. Why lock the ability to edit replies from the main site when I can go to the respective Announcements page and edit my reply from the Boards? I get that the edit lock is there to prevent trolling with edits, and with titles I guess that makes a bit more sense, but the lock on replies confuses me.