As mentioned above, Knuth's algorithms are implemented in many professional typesetting and layout applications. I think the people implementing those applications have great respect for Knuth (and Plass.)

My impression is that the users of those programs are unfamiliar with the algorithms used, so I think it is the latter.

Awesome, thanks! I foolishly forgot to see if there were siblings to my post. (I try and keep a handle on discussions I'm in with the "threads" link.) So, yeah, apologies for missing those posts.