No, we don’t - that’s something completely different. The idea of StackOverflow-style sites is that the best answer is at the top, and other answers are below, based on voting. This works well when people understand how this sort of site works, but a glance at https://help.openstreetmap.org shows that clearly not everyone does - people asking questions sometimes “answer” their own questions with followup questions rather than commenting on answers or asking new questions.
However, it seems a bit daft to turn the feature off just because a few people don’t know how to use it - especially when the creator of every single new topic can decide whether to enable the Q&A format for it.
It’s certainly clear that people want to have those sorts of discussions (this one is a perfect example of where that makes sense) - and there is literally nothing stopping people creating that sort of non-post-voting topic anywhere they want - even where post voting is currently enabled by default. The UI to turn it on and off is “classic Discourse” (completely impenetrable until you’ve had it explained to you) but it does exist.
That’s not a fair comparison. The tagging mailing list (and some of the longer tagging threads here) are basically the B Ark of OSM - a great place to chat about stuff; not so great for “How do I do X?” questions.
It is indeed a shame that some of the functionality in answers isn’t available in comments (and that’s true, by design, in Stackoverflow too), but the ability to comment on replies is extra functionality to the basic site - complaining that it doesn’t do X is a bit like saying that you don’t like the new bike that you got for Christmas because it’s the wrong colour 