Vector algebra triumphed over its non-Euclidean predecessor, and the popularity of quaternions faded. Software engineers, in general, are not mathematicians. They can code an algorithm, but they rely upon others for a rigorous proof of an algorithm's suitability for a task. In this case, quaternions have been shown to effectively solve problems of 3D rotation and interpolation. Perhaps they have, and we just haven't heard from them.
Quaternions lend themselves well to graduate projects and technical theses.
Vectors, by comparison, are straightforward to the point of being boring. There is not much new to say about vector operations in R 3 . Quaternions are a popular buzzword. And their intrinsic difficulty is appealing. Only the most focused, deep-thinking programmers are able to understand and use them.