I can't speak for the "rule set" of this forum for I have not been around it long enough.
That's fine; as I said, I'm speaking very broadly so that this doesn't devolve into a type of thread that needs to be sent downstairs because its focusing on individual moderator action here. So not speaking on this one is fine.
I have been on a lot of forums and have found that on most the ruleset usually means what pisses off any mod at any particular time, or even more often what ever confuses them most of the time, this becomes a violation of the ruleset.
Still, that is a ruleset to a point and fits in with the above.
Sometimes forums have a set ruleset, ala say this one. Its written out and available for all to see. Some can be very exact ("The statement of x, y, or z can cause consequence 1, 2, 3") others can be somewhat specific yet broad ("Remain civil, don't flame people, no trolling") while others still can be extremely vague ("behave, don't cause trouble").
Sometimes there's no real stated ruleset publicly, but moderators upon joining up are basically told what the rules are or the things they should be doing.
Very rarely have I found forums of any decent size have ZERO set rules in some form or another.
Now, sometimes, what you view as something "pissing off a mod" or "them being confused" could be
YOUR OWN bias and
YOUR OWN interpritation of the rules conflicting with that of the mod. That is not necessarily them "creating" a rule, that is the two of your disagreeing on it.
If there's one thing I've learned on numerous message boards that posters have the potential to have
just as big of an ego as Mods and to be just as likely to demand that they did nothing wrong (I've seen people flat out call someone an asshole when personal attacks are clearly against the rules, and then demand steadfastly forever and a day that they did NOTHING against the rules and the mod was incompetent and biased)
This is not to discount that there are some mods that DO just create rules out of thin air and say its part of the rule set or how the rules mean, but as I said, those fall into category 3...those that simply don't care what the rules are.
As for the owner of forums, this too is a question, who wants to own a forum where their personal ego becomes the "ruleset" rather than one where humanity, in all it's diverse and profane glory rules?
Someone that doesn't think like you?
I know this may come as a great and utter shock but everyone is different.
If I create a forum dedicated to Smartphones then I'm going to want my mods to give warnings or take action if someone starts derailing threads about, say, how much people should charge on the app store into a pages long rant about the horrors of capitalism and the evils of those that adhere to the belief. Allowing for "humanity" to be able to display itself in all its "diverse and profane glory" doesn't help, in any way, in having a focused forum dedicated to talking about smart phones...indeed, it distracts from it.
Every forum is different, and with different goals. Those goals are generally shaped by the creator of the forum or the people in charge with creating the rules. Unless the goal of the forum is to be completely, uninhibited, unfiltered, internet anarchy about any subject of any kind in any way, then you're going to have some structure and rules.
Not all people want complete anarchy as the goal, purpose, and focus of their forum.
I imagine an owner of a website would create it because they have an interest in said thing and wish to share it; perhaps altruistically, perhaps capitalistically. The rules they create are what they likely feel will most likely help those aims come to pass along with rules that they create as time goes on as they see certain problems that were not thought of previously.
For example, if your goal is to have a safe, civil forum where people are free from being insulted by others in hopes of that attracting more people than the normal internet message board that is filled with flames, you may enact a strict rule that personal attacks are against the rules and continual use of them will get you banned. One does not have to be a fascist, or a nazi, or some kind of mentally deficient person to enact such a rule. It’s a reasonable, intelligent rule in hopes of potentially growing a forum if your goal is to create what feels like a safe environment. It has nothing to do with “ego” but all to do with what you wish your forum to be and how you wish it to present itself for others. As, in the end, one must essentially “sell” their forums to users by making it unique enough in some way to make them want to come to your forum instead of someone elses.
It seems you believe that all of the internet, in every facet, should be completely 100% open, unregulated, and essentially anarchy where anything and everything can be said by anyone at anytime about anything and as long as its legal then it should cause no trouble. Its an interesting thought, but not realistic, nor preferred I think by the masses that prefer a model where there are places where you can go knowing you’ll talk about a specific topic and just that topic, or places you can go to that aren’t just going to degenerate into a bunch of flames or 4chan like pic spews, etc. I do no think one must be stupid, or egotistical, or lack wisdom, or any of the other childish insults you so mindlessly seem to throw out without ever once seeming to look in the mirror to want that. Indeed, I think it is a mature, reasonable thing to believe that sometimes structure and some kind of authority is not inherently evil, bad, or something to rally against.