Duck Duck Go provides a better user experience. I've yet to see anyone use any other search engine as their main after using Duck Duck Go for a few minutes. Of the dozens of people I know who know a choice exists, about half of them use Duck Duck Go. The userbase grows by about 60% per year, so I expect that within a year we'll grow from about 50% of "techies" like you and I using DDG to about 80% of them, and by the end of next year we'll be at the point where techies still opting for Google are hard to find.
DDG has already decided to start advertising to push their way from just the early adopters and techies into the general public. Everyone has already used Google, so it's not like people will switch to DDG just because it's advertised for them. That'll just make them aware they have a choice, some will take it for a spin, and those people will never look back.
I got a bit off topic... if Duck Duck Go really did lack a better user experience, Apple could always develop their own search engine, or just acquire DDG and give it whatever improvements Apple thinks it needs.