We still teach all sorts of slow and inefficient sorting algorithms, because it helps to understand the core principles of sorting algorithms and computational complexity. I don't think I've ever actually used a bubble sort or a selection sort in anger, but the process of studying those algorithms taught me to reason more generally about algorithms, which is really the entire point. Computer science is a branch of mathematics; mathematics isn't really about knowing things, but about knowing how to work things out.

I suspect we'll be teaching quicksort forever, because it's a really good example of a divide and conquer algorithm.

Obsolete or not, I'd hope it remains in the collection of sorting algorithms tht are presented to students in undergraduate algorithms course. It's instructive to compare and contrast the strengths and weaknesses of these various approaches.