Google cares a lot about user privacy. If only a few percent of their users change their default search engine from Google to DuckDuckGo, they will loose a lot of revenue.
Well, seems like a few people are already looking around for an alternative [1] when it comes to privacy [2]. I can see some effort [3] but I'm not sure if addressing user's privacy concerns is their main goal.
[1] https://news.ycombinator.com/item?id=12035667
[2] http://technical.ly/philly/2015/06/16/duckduckgo-cnbc
[3] https://news.ycombinator.com/item?id=12042613