I think the bang only works for communities: !obviousplant@lemmy.world. Voyager can also handle http links to communities (if the link is in a comment or post body, not a post link): https://lemmy.world/c/obviousplant.
Posts and comments are known feature requests that are non-trivial to implement.
It wasn’t an issue because whenever someone would make a comment, it would “bump” the thread back up the top of the feed (whatever form the feed took). I think the “hot” filter is supposed to take interactions into account, but I think most people just browse top 12/24 hours.
edit: “active” sort seems to do this?