Well hang on, surely the all-on-one link will still be shared. Because that's the link that comes up automatically if there is a post number hashtag.
If you access a thread from your own thread's I'm on or a bookmark you created before, then it comes up as a post number hashtag link. This then translates (when posted elsewhere) as an all-on-one-page link, whether the user uses pages or not.
Surely it would be better to change the software so that links either don't honour the hashtag coding (which most people don't notice and hence don't intend to post at all) or so that the link redirects to standard logged-out layout (20 posts per page) AND respects the hashtag post position.