One minute you have blatantly rule-breaking threads staying up until the bump limit hits and they get archived, the next minute you catch a ban for making a mildly shitposty reply. There's no discernable pattern to it.
In terms of /co/, certain mods are known to police specific threads while outright ignoring the catalog. Toonami General is a prime example since you're likely to see numerous posts get wiped during the pregame hours where everyone is just bullshitting with one another before the show starts. They try and justify it with it being "off-topic," but it's very shallow considering the general threads have existed for 10+ years, determined to be /co/-related by m00t, and only happening once a week late at night while not generating a significant amount of attention.
Also, mods are headline readers who won't investigate any thread if the OP looks to be inoffensive, hence the trend of trolls making fake OP posts to get a thread going and then dumping whatever gore/sneed/porn they want.
Only other site I can think of is Reddit and its numerous boards of political sperging and conspiracies. Which are basically just /pol/, but 10 times worse. But I don't know when that site started to gain that much relevancy.
But thing is, you could apply what you said about /co/ to /v/, just on a lesser scale. Though honestly, if Hiromoot got rid of every board but those two, I don't think anyone would complain = /a/ and /co/ (and their spinoffs) are filled with pedos, the other media boards are hyper spergy as fuck, /int/, /his/, /fit/, /k/, and /x/ are just /pol/ but lamer, /b/ and /3/ are fucking dead, /trash/ is well... trash, /r9k/ is depressing to go through, and /ic/ is full of people huffing their own farts (among other boards that are increasingly getting more and more irrelevant as time passes because all those topics tend to be discussed on those other boards I mentioned).
The blue boards are in a tough spot because their users have aged from teenagers to quarter-aged adults and have realized either through /pol/ exposure or by their own experience that the hobbies these blue board revolve around are fully devoid of soul and have next to no chance of returning to any sort of decency. Say what you will about politics and video games, but they are the hottest things going on right now and have shown no sign of trailing off in the immediate future. Everything else on the other hand has been doing the same shit for 30 years and are now suffering the consequences of kicking the can down the road.
I like using /co/ as an example because they were pretty prolific at the beginning of last decade, full of OC and creators and people actually discussing comics and cartoons. At the same time, the comics industry still had a semblance of credibility, with DC's New 52 reboot and Marvel's burgeoning MCU still in its novelty phase. However, after a decade of embracing cancerous trends and a plethora of bad creative/financial decisions, the comics industry is now a glorified laughing stock being outsold by dumb shounen manga on a routine basis. It affected /co/ just as much; oldfags left in droves, gatekeeping became less important, OC was shadowbanned for some reason, mods and jannies were revealed to be corrupt, and so forth. They whined about /pol/ for years and years while subconsciously subscribing to /pol/'s rhetoric that everyone is a shill or a tranny and that Blackrock is making Disney jump through virtue signalling hoops for capital. If anyone gave a shit about comics or cartoons anymore, you wouldn't see a /co/ catalog being 80% derivative coomer threads.
Another thing: the more traffic a blue board loses increases the likelihood of the board being hijacked by a select few autistic posters who will make the same meme thread every hour of every day in hopes of becoming part of 4chan history.
-Is coffee good for you?
-Would lifting have saved him?
-For me, it's __________
-HOLY CRAP LOIS
-What did he mean by this?
And so on.