You can click on the last post date to go to the last post. The question is what the default behavior should be when a user clicks on the title. Currently XF takes you to the last unread post, which makes sense, however if there are no unread posts it takes you to the first post, which doesn't make a ton of sense if you've already read the entire thread, since if you've already read the entire thread, you are more likely to want jump to the last page and reply.