Okay so here's the thing.
The new generation of writers (i.e 2011ish onwards) like chaos.
But the marketing department (and in turn the modeling budget) likes money.
And marines are money.
If you keep all of these things in mind a lot more of geedubs decisions make more sense.
The problem with all of this Progress™ is that a lot of it is thematically blind with primarchs and chaos just sticking their dicks into everything because primarchs and their new marines make money while the writers love them chaosboys.
Take the devastation of Baal for example.
This giant god damn conflict has been hyped up since forever and no one actually thought that the blood angels would be wiped out, but the war itself was going to be a grand affair with the entirety of the BA's coming together (including freaking renegade chapters) to defend their home.
It was going to be another Macragge level event with the Imperium barely winning by the skin of their teeth and through the countless sacrifice of heroes and heroic actions against a terrible yet worthy enemy.
But how does it resolve with the coming of 8th?
Half of Leviathan just fucking disappears because Chaos™ while Gullyman flies in with his mega marines to save the day, simultaneously annoying both BA and Nid fans.
Like it's not even a criticism of the quality of writing but instead of thematic stupidity.
And now apparently Angron is rumored to be getting involved/stealing the spotlight on Armageddon, one of the like two actually important Ork warzones and it's just getting really tiring having Chaos involved in fucking everything.
Especially after Endtimes.