(author here) We use the device instead of a Raspberry Pi, not for anything too serious: we attached it to a screen and have a small server running with an API where you can write single pixels into the framebuffer (a bit like /r/place)
The "wildly popular" part came when people realized BRCM was dumping these boards cheaper than any existing Linux SBC at the time. The educational angle is long gone.
I would agree that most of the Pis sold are not used for education, but that doesn't diminish their importance in that area.