Yeah, Chaos Marines can hide from the other factions in the Eye of Terror (where the passage of time is wonky). Loyalists fight more or less constantly against everything. You'd expect a higher attrition rate.

Hmm... Yes..... Perhaps, you mortal, have seen the temptations and are on our path... You have clearly never seen the great power of chaos, though! For, if for a moment, you have seen into the warp with my eyes, seen what I have seen... You will know the true damnation of our actions. Continue down this road, and know this, you will continue down the road of damnation, and once down this road, you will never be able to turn back. Not through force, nor through your own free will, for you will love the gifts bestowed upon you by our dark lords.

Chaos marines fight one another until death. For most Chaos Marines eternal war is something they take literally. You don't see World Eaters for example sitting around in the Eye of Terror, doing nothing. Even when they're surrounded by other Chaos legions, there is no safety from war. It's true that the passage of time might have an impact, but only as long as they stay within a part where the warp is stronger. Ongoing crusades into the Imperium and the whole infighting lead to a natural survival of the fittest. I'd say it has more to do with the fact that the minions of Chaos can always return from death, if their gods make it so.

Almost there, child, but a bit further... Within every man, woman, and child, there is the taint of chaos. From the moment of contraception, the taint of chaos is born within you, no matter how pure you make yourself out to be. As you age, your greed increases, and you turn to any means to find a powerful ally, or a way to make yourself more powerful. So who do you turn to?
The Imperium is rotting, and cares not for the little people within it. The Eldar, too pompous to think of you, and too weakened by our dark prince to even survive for much longer. Tau? They are too small, weak, and frail to matter to someone such as yourself. Necrons? Uncaring, undying, and unfaltering in their deathmarches. The rest? Unthinking, brutal savages, not even worthy of my mention or recognition... But chaos, it is there, and has always been there for you. All it take for our generous gods to help you, is for you to help them, through a pledge of your soul.

Generous Gods? They are Dark Daemons They Are the Enemy's You Fool You are Misguided And Corrupt
However If You Repent I Will Give You A Quick Death

They are your enemies. Now do not make that mistake again, because one day one of the four will grant anyone of us daemonhood as a gift and on that day we will ascend to a higher purpose.

i didnt know that one day the dark gods will suddenly give out daemonhood to each and every heretic like its free candy.

and then they complain about us serving a corpse god, talk about blindness.

No, they do not, which is why I said

... which means that there is the possibility that one, not everyone, or even more can ascend to daemonhood. It's something some Chaos Champions have heard about, not like everyone was basically trying to achieve it and therefore trying to get the attention of the gods and the glory that comes with it. Would be something completely new, I suppose.

For the record: No, they don't give out daemonhood suddenly to each and every heretic like its candy. They give out rewards and gifts to those who deserve them and every single champion of chaos wants more of that, up to the point where they become a prince of Chaos. So I don't know where you read something about "suddenly, "each and every heretic" or "for free" - but it seems like you blindly assumed some things there.

Edit: I see my mistake here, you probably thought that by "we will ascend to a higher purpose" I meant that everyone will achieve daemonhood, which is not what I had in mind at the time writing that. Instead the presence of even one Daemon Prince would elevate the meaning of the whole crusade in my opinion, therefore giving every follower of chaos a new chance to proove their worth. I hope that clears things up.

Your putrid, small mind isn't worthy of a reply from one as great as myself... But your sheer incompetence intrigues me. Tell me, will your corpse grant you immortality? Protect you? Give you daemonic hordes with which you may burn entire systems? No... You have none of these thing, nor does your average heretic. Within chaos, those who are deserving receive bountiful gifts from our dark lords. Please, though, continue your empty minded rants for your corpse, I shall sit here and await your laughable reply.