I can't help but wonder if the whole reason Traitor Primarchs are still obsessive about the same thing, literally 10 thousand years later,
To put that in some perspective... written human history in the real world goes back 6,000 years. Closest I can think of as an example is, still being pissy from the invention of the wheel, to the invention of the smart phone, that would only be a little over half of that time.
like, dude, anything you could've grudged with isn't just dead, its so far gone as to be nonexistant and imaginary by this point.
And even more so, in Mortarion's case, where his personality became a total 180...
is because its those points that keep them Themselves. Or what's left.
Like, everything, every demon, every environment, associated with the 4, becomes one of the 4. You can even make the arguement that the problem with the Eldar is because Slaanesh encompasses the concept of being Eldar, and that's why they're being "eaten". Because the concept of Eldar is now Slaanesh, and its only a matter of time before all Eldar is Slaanesh.
The Ruinous Powers have been around since the War in Heaven, billions of years prior, how come there's only mass Daemon Princes now?
Probably because vast majority of them were subsumed with time, leaving only a small handful.
I imagine it has something to do with why they were elevated in the first place. The moment that reason no longer stands, they'll be eaten.
Magnus and Mortarion only go for their Grudges, now a severe obsessive fixation. They're at the most risk of just being Gone, just another aspect of their respective gods once that grudge is let go or done.
Fulgrim is an... interesting case, in that I'm pretty certain his is avoidance, not grudge. People don't pull the perfection stint, or the sensory esctasy stint, unless they're forcefully trying to avoid something at the constant edge of consciousness.
Which might say something about the state of all Eldar.
Angron is just, one step from being just an avatar of Khorne. Ironically, it might even be the Butcher's Nails preventing that last step, because there was little to work with before, and now there's not a whole lot left. The thing that killed him in life is the very thing preventing his total subsumption.
Perterabo is in an interesting case in that, he's running on the Grudge, but not to a power. Good chance that if you don't have a ruinious power to abide, you either get subsumed by all four, or you just, fade into the warp.
I have no fucking idea what's going on with Alpha Legion, and I'm not gonna really pretend.
Then there's the increasing mutations in the various Chaos Marine Legions. The Thousand Sons are becoming bird monsters. The Death Guard are plague monstrosities and are getting worse. Like, they're just gonna end up being daemons of their ruinous powers when all that humanity runs out. I think the only reason it hasn't gotten that far is because of the Primarchs--So when they go, everyone goes.
Because if it was that easy to be a Chaos Entity like that forever, there'd be more entities from across all of space time, not just Chaos Marines.
Prolly even quite a few of those xenos that the Emperor had xenocided. Or maybe entities that were killed during the War in Heaven. Eldar for certain.
What's going on with Chaos has a Time Limit with those involved.