Ask HN: How did the Arduino Pin Header eat the world?

I have a several boxes of embedded boards in front of me. There are ~100 boards total, from: NXP, Intel, Renesas, InnoPhase, RealTek, ON Semiconductor, Nordic, STMicroelectornics, Atmel, just to name a few. All but ~10 boards have an Arduino Header on them. The remaining 90% conform (roughly) to the standard Arduino header: Rx/Tx uart on pins 0/1, VIN, 5V, GNDx2, and 3.3V pins, and the rest GPIO. I can't find a good explanation as to how a tiny foundation started 16 years ago became the dominant interface of the embedded world. Does anyone know?