I don't know either. If any FP regulars want to chime in about why the OIFY was such a cesspit, feel free, but here's Encyclopedia Dramatica's analysis on it (and while I don't like using it as a source, there's a kernel of truth here - probably)
OIFY breakdowns tend to be really scattershot because they depend a lot on who wrote them and when they participated in it. Most people would have their fun in OIFY for a couple years and then fuck off to some other forum or private spinoff group, rarely to return. Personally, I have never seen an explanation of it that totally does it justice. Odds are, you won't see it in this post either, but i'll take a crack at it anyway.
I guess you can kind of break OIFY down into different eras. Again, it largely depends on the person posting, because they have an intimate knowledge of their heyday, some general understanding of the previous era, and a half-imagined cliff's notes version of what happened after they left. I'm no exception.
If I were to break it down myself, the first era was the porn and furshit era. With Facepunch being an SA ripoff forum, there were a lot of FYAD seeds planted pretty early on. As far as I can tell, it was simply a small group of people calling each other faggots when they werent posting elsewhere on the forum. Also, because it's Facepunch, people were ironically or unironically posting all kinds of furry shit. This era is hard for me to pin down in detail because despite being around forever, I know absolutely no "oify guys" from this period. It's like they all left the fuckin planet. Anyway, I'd pin this at like 2004-2008, ending around the time when user MiniCooper shoved a huge butt plug up his ass.
OIFY people seemed alright, aside from their confusing jokes based around spam and references to shit they made up. Perhaps I am lacking lore, but I do find it strange as to why they're hyped as the great evil of the site.
This is the second era, and the era I was most active in. "jokes based around spam and references to shit they made up" is about the perfect way to describe it. Not to be another "i was personally responsible" guy, but a lot of the brain dead in-jokes you saw can be credited to me.
I should mention that CCOF had absolutely dominated the OIFY during this time, and we totally piggybacked off of the existing perception that the OIFY was "the great evil" of the website. We leaned into that very heavily. Truth be told, most of the retarded shitposting you saw was circlejerk nonsense we made up in the steam group chat, which we would carry to the OIFY. We were also very well connected with a lot of the moderators at the time, which allowed us to frequently take our horse shit to the mainline forums without a real fear of being banned. This is probably why people saw so much OIFY shit in GD around this time.
It is interesting to note that either garry or Hezzy peeled both Craptasket and Greeman from CCOF to be forum moderators. Despite being two of the founding members of CCOF, they were somehow able to immediately pivot to being professional. Really, it baffles me to this day. After that, there was maybe a year of fun with custom banners, and craptasket himself was curating oify content through stickies. Both of those dudes slowly faded away from ccof, and ccof slowly left facepunch as a whole around 2011. At this point, a posting vacuum opened.
This brings me to the "last" era, at least in my mind. To be totally up front, I don't really know much about what went on much after 2012. I did start noticing that the gap was slowly filled by people who weren't CCOF, but wanted to post in the same spirit. Noble goal I guess, but what it quickly turned into was a bunch of people posting shallow shock value threads. When I saw that each thread had single digit replies with very little jokes, I punched out for good. Nine years is a lot of time though, so maybe someone can fill this part in. I sure as hell don't know.
Y'know, I was browsing the Facepunch wiki and I just remembered there was an old archived thread from February 2019 where people seethed over that gore thread and demanded that the mods bring them your blood. I'll see if I can find it.
Edit:
Here it is. Two years and they still haven't moved on, impressive.
Damn man, by the looks of that thread, I dont think there was anyone of repute to really stand up for the OIFY at the end.
If there's one thing I can say about the OIFY from start to finish, it's that it was allowed to exist based on the connections made between heavy-hitting OIFY posters, old gold members, and Facepunch moderators. I recognize a couple old OIFY veterans in that thread, but even they said "aw fuck it" because they stopped posting there years ago. On top of that, most of the old-guard moderators who had OIFY connections in 2011 had already left Facepunch. The only dude left to step in was craptasket (and to a lesser extent, postal), but neither of them had a real connection to any OIFY posters in 2019. In a way, I understand why they didnt go to bat for it. It would have been a pretty untenable position at that point.
Regretfully, it looks like the OIFY is one of many things that has been swept under the all-encompassing "times have changed" rug.