In 1977 you didn't have high blood pressure until you hit 165/95! That must've cost countless lives.
The big medical organizations that set guidelines are very conservative, moving at a glacial pace and only in response to overwhelming evidence of benefits and safety,
So since then the definition of high BP has been drifting down to where we are today, that is, with. a few special exceptions, anything over 120/80.
You're right, those lower numbers have shown better long term health outcomes, but we're now so close to the bottom(where certain risks start to increase), I doubt we'll see future universal guidelines go below 120/80. As more studies are conducted though, I think they'll be able to specify individually personalized BP targets below 120.
I heard one top preventive cardiology researcher on a panel say in response to the question "what does the evidence show about how low the ideal BP is?", "As low as you can get it without falling over."