Lots of solid points, Sir Beregond.
As far as OCN goes, the rep system, or the lack thereof until recently, likely pushed quite a few users away. Twocables just came back after a year hiatus, though there is likely another reason for that one.
Overclocking in general has become less necessary. When you have threadrippers and other high core count processors killing it in multithread as well as having solid single core performance, the need to overclock is becoming less of a necessiity. Not to mention, the increasingly high thermal densities is making it more expensive to cool these processors. Performance is going up, dies are getting smaller, but power consumption has not been going down as much, especially with these intel 14nm fryers. You can't really get far with an air cooler nowadays compared to a custom loop. It's always been that way, but now it's getting to the point where even on mainstream parts you need better than air cooling to keep the processors under control.
Graphics cards are less fun since they're getting locked down now. We can still have some fun with AMD cards by changing the PL tables, but they haven't been really competing with NV very well lately, at least in the high end. The flagship NV cards have to do with bios swaps or hardmods to get up there, and the provisions they have in place makes it a hassle getting anywhere.
Memory has stagnated a good bit. While it's reassuring to see news about G.Skill breaking another record, it takes a golden sample to even reach those speeds, and most of the time it's at timings so bad it's not even worth considering. On the other hand, memory overclocking does do really good things on Ryzen, since IF really benefits from faster ram as well as tight timings.
Media is also changing. People will now go to youtube or reddit for discussion instead of these old antiquated forums
While people like linus and PDP have brought tech to the mainstream (I know there are more don't slap me), we lost the detailed analyses in return, especially with some of the noteworthy ones moving over to AMD/Intel/Whathaveyou. The popular tech channels often review parts at a higher level than most veterans are accustomed to, and that's fine for the mainstream who just wants a basic rundown. Though, I may be putting words in people's mouths at this point.
And if you've noticed, there aren't as many review websites getting samples anymore, and some websites won't have a review of a newly released part weeks or months after the launch. It didn't use to be like that. The less exposure, the smaller the footprint, the less attention it gets.
Ultimately, there will still be things to overclock, but the the cost of doing it are higher than it used to be and the gains aren't, which turns this hobby into more of a niche than it used to be. High end cards are really expensive now, processors are getting up there as well, motherboards the same. Thankfully, ram and drives are a lot cheaper now.