Used to find the very idea of the Night Lords deeply, painfully cringe and like...yeah there's still a certain amount of goofy ass shit going on there but their entire story is full of pathos.
Like imagine you escape your nightmarish home planet via a highly romanticized job that provides for all of your needs, but you're stuck with a gene-father who's
-basically 9ft Self-Righteous Richard Ramirez
-extremely mentally ill and growing worse by the minute
-filled with nothing but seething contempt for you and your brothers (partly justified as you guys are the fucking worst)
But you're indoctrinated with a combination of Imperium propaganda and trauma bonding to constantly seek your abusive fathers validation, so you carry out his fucked shit on command and become universally reviled for it, including by said father.
Then your father decides to destroy your planet and secede from the Imperium, which you have to go along with. What are you gonna do? Stop your nightmare dad?
Now you and your god awful found family are truly isolated; your only options for companionship are various horrific weirdo Chaos Marines and whichever creepy unstable assholes you got stuck with in your company. Well, also your dad, who is still very much a 9ft tall mentally ill guy who despises you.
Then an already bad situation shits the bed further when you lose the civil war, your dad decides to do suicide by cop and your legion fractures into a hundred scattered companies.
You're pretty much just a goth pirate now, which sounds dope in theory, but absolutely isn't in practice.
Everyone hates you, you're stuck with the fallout of your dead dad's decisions, you can't revert back to normie life due to being a homeless transhuman freak fugitive, you can't ditch these losers to switch to a new legion because the Loyalists will execute you on sight and joining up with Chaos means being enslaved by demons.
You have no plan, no purpose, no central leadership, your people/culture are an endangered species; it's just you and five shithead creeps floating through space until someone finally manages to chop your head off with a power sword.