I concur, I concur!-however, I believe that your (lilaaronuk) view is somewhat more optimistic than mine. I would elaborate on that but it would likely be perceived as petty, bullying and perhaps mean-spirited all around (and it likely may be to some degree).
I never considered the angle that you have suggested as being the reason for such lowbrow content, and while it seems like a potentially plausible explanation there are other sites that operate slightly different content-wise and yet suffer the same syndrome in the forums.
A prime example is DailyDiapers.com. They have a huge archive of photos as well as new ones being listed fairly often. There are no requirements to post or contribute a thing to harvest these goodies; and yet, the forums are inundated with the same exact drivel as you will discover in almost every other forum no matter the design.
I'm not terribly familiar with the site that you mentioned, and I don't claim to have experience with every site offered. I do believe however that I have located and have 'test driven' most of the popular sites. What I have discovered is simply this, like mentioned above with DailyDiapers.com, no matter how the rules are designed, the forums are always filled with the same content. You could be a member of five different sites and never hear anything new.
Here are some theories of mine as to why this is: For the most part, with the exception of a few actual new members from time to time (as opposed to duel profile identities) it is the same lot of folks filling every forum membership on each of these sites. With the same people, you suffer a quick stagnation of interesting topics and the forums turn quickly to bland, repetitious fluff. There is nothing new to cover, and as the fantasy life of diapers holds strongly onto each person, the want to converse about things past a certain depth are unlikely as delving too deeply can take one out of that moment, i.e., it is almost purely masturbatory in appearance. With most people approaching it in this mindset, as well as the situation of stagnation mentioned before, you'll find mostly just short, empty snippets of exchange that one can use to reassure their fantasy. Hell, mention the word paraphilia and some people get downright snitty as it threatens to usurp this realm of fantasy.
But this is simply my assessment, and as we all should know that trying to assess anything about the motives and whatnot of others while on the internet, a vast and still untamed landscape, we are merely making educated guesses at best.