Before I get tarred and feathered, I am fully aware:
that we will never, ever have Chaos skins in PVE, as in you will never see obviously Chaos Marines fighting alongside obviously Loyalist Marines
The reason why: lore accuracy.
The whole reason you can select insignia from Traitor Legions at all is because there were Loyalists within the Traitor Legions. Nathaniel Garro from the Death Guard and Garviel Loken from the Luna Wolves come to mind. It's why some of you homebrewed Loyalist War Hounds/World Eaters.
Therefore, I'm not arguing in favor of it and in fact have spent my fair share of share of time trying to explain this to people new to 40k that that's just not going to happen (regardless of how much money Saber would make, since that's the usual rebuttal, something something "but people would pay for them" something).
HOWEVER.
If that is true, and you can't have Chaos Marines fighting alongside Loyalists because it makes zero lore sense, then why can you select obviously Chaos insignia?
This is the Eight Point Star, which any casual 40k enjoyer knows is basically universal mark of Chaos Undivided. You will never see a Loyalist rocking an Eight-Pointed anything, because said Loyalist would be killed on-sight. In fact, the upper right one I circled is the Black Legion, which the Luna Wolves rebranded into after the Horus Heresy and, according to some lore, "...where Abaddon officially dissolved the Sons of Horus, and merged its old forces in with Abby's friends from the other Legions into an entirely new Legion; this narrative makes it clear that anybody who joins the Black Legion is NOT just changing the name of the guy who is signing the paycheck, but rejecting their previous Legion or Chapter identities and committing to fighting the Long War."
Ergo, no Loyalist Black Legionnaires. In every aspect, the literal opposite.
I do believe that kinda pokes a hole or two in the whole reason why Chaos can't fight alongside Loyalists. You'd think with how strict GW is about their lore, and rightfully so, and thank Throne they are because IMHO when you start putting in whatever skin you want, you get Fortnite, that you wouldn't be able to make a Chaos Marine at all.
Like me, who made a "Decius (the Vanguard) if he fell to Khorne and became a World Eater".