I'll have to file this under "I dunno".
What I mean is I agree that it sounds like this might be a cultural thing, I'm intrigued by Japanese culture but I can't really say I understand it, let's say I know enough to know I don't understand it. It seems that I don't understand what's going on here, so I can't really make a comment on it.
That forum discussion keeps suggesting that this is an attempt to control "the maniacs". As if this isn't so much about photographers getting in the way, but people who go to far and who might bring tripods with as part of their excessive fandom. What I mean is they make it sound like this isn't about photographers, but more about fans who go too far and intrude upon the experience of others who ALSO might bring camera gear.
The part I want to highlight is that one of the posters in that thread provided what looked like a luggage tag.. well, a paper tag attached to a looped rubber band, I don't know what it's intended to be attached to. But it spells out the tripod restrictions, including the term "unipod" which is a new one on me (I assume it means monopod?). It says no unipods, tripods, hard carrying cases, or other such equipment.
This is part of the enigma. To me a hard carrying case is not in the same category as the other items. It almost sounds as if they're suggesting people were using hard carrying cases as a base to take pictures, but I'm guessing that's not the intended meaning. Presumably it means people were going into the park carrying a hard carrying case full of camera gear. It kind of contradicts my impression that this isn't really about photographers at all, but rude people carrying cameras (I hope the distinction between the two is concepts is understood). So maybe it really is about photographers hauling in loads of gear and getting in the way of other guests. I would have expected that to be less of a problem in Japan, but perhaps I was mistaken.
For that matter I really wouldn't have expected anyone except a professional who is there to do some serious commercial shooting (which is something park management can prohibit right there) to take a hard case into the park. They're heavy and bulky, you use them to transport gear, such as by plane or car, you don't walk around with them. The fact that they included it suggests that people are doing something there that I haven't really experienced in the states, and doing it enough that it warrants special restrictions.