I’ve very rarely seen engineering managers that didn’t come from being an engineer. Most lower level manager interviews (at least in the valley) still involve a significant amount of technical questions to weed out people that don’t have a solid engineering background.

If you are talking more about executives this has also been true at places I’ve been. Engineering VPs mostly were also engineers at one point, although likely long ago. Conversely I’ve known very few engineering managers / directors / VPs with MBAs.