I suspect is just a bug: the ligature tables were copied from the regular variant, and perhaps no one noticed for some reason. Maybe the assumption was that the renderer would turn of ligature processing in monospace mode at the time, and the reference renderer did that?

I can't find any examples now, but I'm positive that there have been "coding" fonts which do this that have hit the front page of HN. Highlighted as a feature in the screenshots, even.

Another example of form over function, to the utter detriment of function, IMHO.

Perhaps Fira Code?

https://github.com/tonsky/FiraCode https://news.ycombinator.com/item?id=10764527

But I think it's different: it uses double-width characters for two-character ligatures, so this doesn't break alignment.

It's truly amazing that people can like different things, no?