DDG's main schtick is that they don't track users. It would be nearly impossible to match Google or Bing's ranking relevance without using signals derived from logged user traffic. Their core principles essentially ensure they won't ever be a serious competitor to the leading search engines, unless a lot of people decide that they're willing to sacrifice a lot of relevance in their search results in exchange for stricter privacy.

I'm quite sure they used to use google in the past

> Why can't DDG just cut their losses and invest in building their own index?

That's far from trivial task.. Scraping and using other peoples results is easy, building and scaling a huge database like search index is one of the hardest problems you can find.

Ok that's fair. But in that case, I don't understand what compelling way DDG is differentiating themselves from other search engines besides a few cool, nice, thin value features.

.. that's almost exactly what I'm thinking too ..

Because right now there are only 2 companies in the world with sufficient technical chops to build a competent end-to-end modern search engine. It's a HARD problem. No startup can do it.