DDG, in fact, uses Bing. [1][2]
[1] https://www.reddit.com/r/duckduckgo/comments/4lgda4/duckduck...
[2] https://www.ghacks.net/2016/07/01/duckduckgo-yahoo-partnersh...
[1] https://www.reddit.com/r/duckduckgo/comments/4lgda4/duckduck...
[2] https://www.ghacks.net/2016/07/01/duckduckgo-yahoo-partnersh...
If they grow too big Google will just switch them off..