The frustrating thing is it's not mysterious. Everyone knows documentation matters. The failure mode is that it gets deprioritized the moment the team is moving fast, which is exactly when it matters most. A decision made under pressure with no record becomes a source of technical and organizational debt that compounds quietly.
The teams that scale well seem to have internalized documentation as a forcing function for clear thinking, not just a record-keeping chore. If you can't write down what you decided and why in two sentences, you probably haven't finished deciding.
I'm sure they were in a constant struggle for survival and had to "move fast" to stay afloat, but their technology is more than a decade in the making.
If it works, it works, but I really wish companies and founders would just be honest about how and why they succeed when they do, instead of everything needing to be the constant projection of a desired image.