Because it can help people realize they might have read this before (I had), which in turn can affect how one prioritizes which articles to read.

Also because "it's how it's done around here": the site is about news so it makes sense to at least tag possible re-posts to flag them as "not quite news yet still interesting and recommended reading".

Yes, because avoiding lots of LOC by relying on tons of external libraries is the new 'doing practically nothing'. /s