From what I know (which is not well sourced), the big problem with K is that it didn't have an open and accessible interpreter for a long time, and that hampered adoption. I know 5-6 years ago I was interested in it, but couldn't find any interpreters that were free for non-commercial and commercial user (it was mostly work related interest), and didn't stumble across Kona[1] at the time. Not it's on my list of languages to look into again, but that's a long list.

1: https://github.com/kevinlawler/kona