Cooperation: It's been some time now since we were first contacted by DuckDuckGo regarding the possibility to partner with them in order to share a percentage of the revenue that they make from the traffic originated on their search engine links ...
So DDG made a deal they could afford and got their partner to hold water for them and link to one of their PR websites, they've been ramping up their marketing efforts to try and capitalize on certain fears, which I suppose is logical.
Generally speaking I think ddg went with the "we don't store data" route because it's the niche they were left with and that ultimately means their search won't improve beyond a certain point.