Ads of course. Bot not as greedy as google. Not tracking every fingerprint of you. They just show sponsored search results according to your search terms at that moment, in contrast to your whole browsing history/habits.
I use ddg as my main search engine but disabled ads because I can't stand them. I wish they'd let me pay for the service. "If you're not the customer you're the product". I want to be the customer.
If you're willing to pay, you're likely worth more to advertisers..
Advertising. But not via tracking and personalization. They show ads to you based on the keywords you used to search and don’t follow you around the web.