1. Search is hard and fascinating.
2. There's built-in conflict. Google is a huge near-monopoly. Journalists and their readers love conflict. It's the heart of any good story.
3. Most of the time, building a general purpose search engine requires a really substantial amount of capital and technical expertise. That means there's big risk involved. This ups the drama quotient. See #2 (DDG being a very big outlier here).
Don't forget the institutional imperative: Google is a competitive threat to people who buy ink by the barrel. Anything that takes them down a peg is newsworthy. See also Facebook, who do not have the "we're do-gooders, leave us alone" PR shield that Google assiduously cultivates.
Actually, I think that's wrong. A very small number of media owners think that. And even they did, they'd have to think that search in general, not just Google is the threat.
Anyone writing about tech and especially those writing digitally knows that search drives tons of traffic. And no tech reporter I know would ever take direction on coverage from the business side of their publication.
Blekko got written about because they are a great story.
I don't think DuckDuckGo has received the same amount of coverage, actually, so I'm not sure all search engine launches get such enormous productivity.