I don't think is the reason Keybase faded (although I agree that they shouldn't have chased blockchain fads). I'm pretty sure it's because they were bought by Zoom and had all of their engineering talent repurposed.
It's my personal opinion that they had lost their way before getting bought by Zoom. Mostly gut feeling from the actions and words from senior leadership.
But you're correct, Zoom's purchase was the death knell.
