Because I use two "Recent tabs", one public and one only for me (that is filtered out before I upload). The latter is the normal list but the former only shows specific tiddlers and - most importantly - in the order I specify using the "recent" field. I am presuming that visitors are peeking at the Recent tab to get an idea what is new - but the thing is, I modify/tweak my articles but often the tweaks are not worth calling attention to in the way that a "last modified" list does. If an old article is worthy to get to top from my modification, I update the recent field (via a quick update button that is also not uploaded to the public TWaddle).
Overall I'm hoping to eventually find a better workflow, but so far this is the best I've got which means I write a lot of stuff, tag them Unfinished, until they are ready for publication when I also add the "recent" date. When there is enough finished stuff for me to feel ok, my millions of readers cannot wait another day without new wisdom, I publish.
<:-)