Why? I'm being serious.
Everyone assumes that our lot in life is to be productive. For Americans it seems we need to be as productive as possible. It's untenable.
The most productive person is the one who dies at 40 because they didn't get enough sleep because they drank too much caffeine and augmented themselves with other drugs to maximize wakeful productivity. Is that worthwhile?
I can definitely see a problem with spending considerable amounts of time keeping up with social media because ultimately the thoughts, pictures, and videos posted by your "friends" aren't important. You, them, and everyone else will have long since forgotten what was posted in a week and nothing of value will be lost.
On the other hand, "keeping up with the news"--especially news in your industry--is important. There's a lot of things going on all the time that could make a huge difference in our lives and careers. Things we need to stay on top of not just because we care but because they have impact.
I don't know about you but at my job it is a common occurrence for me to solve problems with tools and techniques I've learned about through sites like HN. Keeping up with these sorts of things also gives you insight on how to schedule things. For example, if you just read that the next release of ProductX will include a feature that you need you probably won't bother to spend time writing your own implementation since it will be obsoleted soon.
Then there's the entertainment aspect: What's wrong with "wasting" time if you're enjoying yourself? I enjoy reading the news and the occasional entertaining Reddit post. When I laugh at a meme was my time truly "wasted"? Or perhaps the time I spent trying to discover "something good" was wasted?
"Getting things done" in spite is the opposite of happiness.