What the fuck are you talking about? Your analysis has no basis on reality, I have never seen a clear pattern of warhammer avatars talking as if they were space marines, never have I seen a post of a space marine pfp that says something along the lines of:
"By Iron oath and tempered will, I have commited a grave miscalculation and posted videos on the 'Pictures that made you laugh histerically' thread, yet in solemn defiance I stand unbroken against an onslagauth of angry mods"
Nor have I ever seen someone with an anime avatar say something like: "KYAAA!! With that shitty post that got a lot of dumb rating I accidentaly triggered my ultimate life destruction! But with the power of kawai desu friendship, I'll turn this trainwreck into a victory on my next post!!"
I think this exists only in your imagination, and other people are playing along due to some sort of group psychosis because they don't like anime or warhammer, people don't adopt the attitudes of their avatars my man, imagine if I made a post saying that people with cat avatars seem to be confident, ndependent, selective when it comes to who they chose to be nice with, and they are not needy, because that's how cats are IRL.