Out of curiosity, what about it seems to discourage extended discussion -- is it something like the threading structure

I think the threading structure makes group discussion of a point of contention unproductive. The latest replies are dispersed throughout the page, and there is limited nesting in practice. Lengthy back and forths are left to the small handful of those posting and getting reply notifications.

As far as technology for discussion goes, The Web Zillion Point O has miles to go to catch up to the technology of Usenet and trn.