The best reason I can see for this rule to remain is because I assure you before any thread on this forum would get to 800 posts it would be full of spam, full of off topic posts and just generally a mess. And what moderator at that point would want to sit down to 800 pages of edits and deletions and such to try and keep it open? Not one of us. We would lock it and that would indeed be an abrupt end to the discussion because we would not allow another at that point.
Keeping it to 200, I can come in after not being here for 12 hours or 2 days and without knowing what happened the last two days in that thread I could read through it for problems in a short amount of time, edit out problems and keep it open and thus closing it at 200 another thread would be possible because that thread went ok.
Restarting a thread almost always brings it back on topic, has more new members willing to read the entire thing and helps the moderators keep things tidy and civil and on topic.
Nope, we don't have to do it this way but as you can see a large number of our members are used to it. Those who are new sometimes squawk about it but after a bit they too seem to like it. In the end, it harms nobody, assists the moderators and newer members in keeping up with a thread or subject and for this forum and it's members...it just plan works.
I like it. I'm even spoiled by it as I despise finding a 1000 page thread on a forum about something I want to know a bit about and having to wade through pages of "I like pie" and "rick roll" and senseless emotes to find what the thread was supposed to be about.
:shrug:
Anyway, I do believe in questioning authority but in the end, it is Bethesda's choice and we all agree to that rule when we join so it should be no surprise. I'm just sorry they did not institute the moderator tool to shock users via cyberspace when they question us instead of the 200 post rule. They thought we might abuse it.