It’s just that the hyperlink isn’t featured, in the left sidebar, under the “Categories” section. In that case, there’s plenty that isn’t there under the Categories section.
The tags under Categories often change based on the changing popularity of the topics on LetsDiskuss.
Digital marketing is a popular topic on the platform like sports, finance and health & beauty.
LetsDiskuss, even with a massive user base already, is still growing. It’s still in its growth phase. So, as we go about with more user-generated content, including under the digital marketing tag, you will likely see the category more prominently on the site.
That said, at present, there are many (interesting) questions and answers under ‘Digital Marketing’.