I had this same thought. I did realise you can click on the date of the last post (e.g. where it says "today"), so there is a workaround. But that's not ideal for less frequent users who may not be willing to look for the workaround. And a button would be easier for everybody.
maybe as a quick, interim, measure, just change the Colour of current, aforementioned, link that exists in the date. Change it to that blue colour that people often associate with links.