What’s Sad Is That Regulus Would Have 100% Known That Sirius Would’ve Never In His Life Betrayed

what’s sad is that regulus would have 100% known that sirius would’ve never in his life betrayed the potters and i think about that a lot

Danger and the Black Family

"It's ideal for Headquarters, of course. My father put every security measure known to wizardkind on it when he lived here. It's unplottable, so Muggles could never come and call — as if they'd ever have wanted to — and now Dumbledore's added his protection, you'd be hard put to find a safer house anywhere."— Sirius Black regarding 12 Grimmauld Place

It's common in fanfic to see Grimmauld Place as a magical fortress, the ancestral fortress of the Black family, with wards (I know that it's a fanon term, but it's a useful one so don't @ me) as ancient as Hogwarts itself. And that make sense, after all, doesn't Sirius tell us so in the books? Well yes and no. Sirius does say that the house is warded, and heavily so ("every security measure known to wizard kind"). Sirius is exaggerating here, since the house doesn't feature protections like the Fidelius (until Dumbledore added it), but it's meant to show that the House is heavily protected.

The bit I'm interested in is the part I highlighted in the quote above. My father. The protective spells were not modus operandi for the Blacks, they're something new. It isn't him renewing spells his father cast either, since Arcturus dies after Orion. It makes sense that they're not standard procedure, after all they're wealthy and influential in the government. As pure of blood as one can be. They consider themselves wizarding royalty. Why would they take measures to protect themselves from those they consider their inferiors? Now, the question that naturally follows is: What changed? What prompted Orion to feel threatened enough that he felt the Black family residence needed reinforcement? I have my own elaborate headcanon about this, but I'd feel interested in hearing other theories first.