Or those houserules are bullshiting themselves and everyone else. And, more importantly, they don't aknowledge and take credit their own hard work.
I used to have a guitar, originally made by Yamaha. Over the years, I've changed pretty much everything on it. The only original part on it is griff. I've replaced the pickups, then the deck, then pickups again. No way in nine hells I'm gonna call her "Yamaha guitar" at this point, no. I built it, with my own two hands and she deserves to bear my name.
Not to mention that system's purpose is to create a fitting experience just by the way the rules work. You grab Blades in the Dark, you get a game of daring scoundrels executing bold operations and getting entangled in some deep naughty word. You grab Monsterhearts, you get a game of teenagers coming to peace with their gender, race and sexuality and embracing their identity. Just because the mechanics are pushing the story in the desired direction.
But I don't think I want to explain game design 101 for the millionth time.