why media like bad news?

That's what people want to read about.  Be honest with yourself; which are you most likely to read about and talk to people about, neighbors helping each other clean the roof gutters or the horrific murder of a toddler 200 miles away?  We are animals in the end and are highly attuned to danger which is why bad news catches our attention.  However, this is not so good for us if we can't discriminate between clear and present danger, far away, past, and speculative events and ran them accordingly.  You could argue that the biggest problem is that reportage, which is a social good, costs money and the current model relies on adverizing which means that there's considerable pressure to push the most negative news as this enagages our attention - which is what the advertizers are paying for.  For your own mental health you should limit your own news consumption to once or twice a day and avoid scrolling updates and rolling news.  As soon as you notice a story repeat in a day it's time to turn the news off.