What I mean by it: Someone advocated for the solution (it ended up part of a product) and since now it's deprecated those advocacy efforts weren't successful enough to induce adoption. By your words there seemed to be only a single person, but from outsider's viewpoint its impossible to say how big push there was.

"Nobody knows or likes Prolog" is exactly the reason why I refrain from using Prolog in professional environment. I can use it, I like it, but unless I have full team of people committed it's an empty effort (even harmful).

So yeah, if smart people failed to convince other smart people, there's something wrong with it.

And in my view is people don't get to like it because current sources aren't good enough. There is documentation but it's not clear what the target solution scope is (and rarely people professionally implement Sudoku solvers), what the benefits are and what are the success stories.