Since DDG also sources their organic results from Bing, I wouldn't be surprised if there was also a contractual obligation that required DDG to use Bing ads to reduce the cost they pay for the search results.

Over the last few months I have been working on an alternative search engine. Maybe naively, I thought the most difficult part was going to be to convince people to use it, but the real challenge if figuring out a way to monetize the service in a way that maintains privacy and respects users. The more I go down this path, the more I realize the next big search engine will be one that provides better results AND comes up with a better way for monetization.

I wrote a little about it here [0] if anyone is interested.

[0] https://coil.com/p/runnaroo/Privacy-and-Search-Engine-Moneti...