This, in my mind is effectively a bug, even though it's meant to be a feature.
Comments are not for extended discussion; this conversation has been moved to chat.
Of course I understand that people may not want to trawl through many comments, removing an entire body of comments to chat effectively terminates what may be really salient and useful information.
In fact, if there were some form of UI ability to conceal/disclose threads, and to indicate just how many comments there are, the argument in favour of moving to chat as provided by @bilbo_pingouin would be moot and irrelevant.
Of course the reasoning appears good. But evidence (go have a look) is that moving to chat is a discussion killer. If we are hear to exchange ideas, it seems counter-intuitive to deter people's contributions to another's answer and effectively reduce their contribution to Upvote/Downvote/Not-bothered.
On many other stackexchange sites, and particularly the original one as well as maths, the answers are almost always accentuated and informed by the comments.
Note also, that on this site, an initial downvoting of an answer I gave (see question The Infinite Sea, how narrow can that be?) switched over to a strong upvoting in light of the comments - but the voting was effectively killed the very moment that the entire body of comments were moved over to chat.
While the chat is not visible on the page, in context, it may as well be called 'trash'*. And while admins may see it as beneficial to encourage the discussion to take place elsewhere, they are effectively saying 'move along please - nothing to see here anymore'.
* I have yet to see (or experience) a chat that has lived on after it has been moved out. This itself is a clear steer of it being nothing short of a trashcan.