Well it wasn't really a teaching revolution. It was a marketing job around a YouTube channel that purported to be a teaching revolution.

The thing is people want more than material. They want the material to be accredited and examined. Otherwise there is no demonstrable credibility from doing it.

And there's a whole world out there of higher quality material with has that accreditation and examination structure around it. And it existed, sometimes for decades in the case of The Open University, before Khan Academy appeared. But it costs money.