Maybe it is because happy people do not consume the news? Happy people tend to have full lives and are therefore too busy to waste time ingesting news about events that are not going to personally affect them. Whereas, I can only speak for myself, but when I am down (like right now), I spend lots of time doing nothing but browsing news aggregator websites and leaving comments like this one.
And of course, negative news would resonate more with a person who is in a bad mood.
And of course, negative news would resonate more with a person who is in a bad mood.