Comment by ajkjk

Lots of engineers are lapsed physicists who have hobbyist interest in this stuff.

Also lots of HN readers are actual physicists or mathematicians. It's not all techies.

Also, lots of engineers have at some point learned some computer graphics and so been exposed to quaternions in that setting. Since they're mysterious and hard to wrap your head around most people don't really 'get it', leaving a sort of standing curiosity that articles like this tap into.