But yes, it's entirely an exercise in trust. There is nothing stopping them from being nefarious with this collected information, except their brand. Someday they may sell out, or maybe they already have, who knows?
Thing is, nobody has your best interests at heart. These are all profit-driven enterprises and everyone has their price. DDG just markets itself as less evil.
You don't want to trust anyone? Then don't. Block the trackers, rotate through VPNs, always use incognito, etc. Or just accept it as a cost of searching and move on with your life... your profile is just going to be one of millions anyway, even if they do track you. At least they don't have the cross-product integration and remarketing that Google's billions can buy.
At the end of the day search is an expensive endeavor requiring constant spidering and curating and anti-spam efforts. If you get it for free, you're the product. DDG isn't magically above the economics.
On the other hand, those of us who do know what can be done with that info choose another path which is not about self judgement of our online actions. We are aware that data can be used in various ways to analyze our behaviors or the things we are searching and finding. Depending on the services that we use, we may be "targeted" with relevant ads, emails, or other changes in behavior by the sites we visit.
Preserving privacy on an individual level is about using services or applications which we understand AND can control. Trust is lost when we don't understand applications properly or control how they react later on.
Any service or application, which is not self hosted, should allow users to configure or DELETE information which has been sent or gathered by the user. That site or application should also have a clear revenue model and privacy policy that indicates the site or application owner will not change the model or behaviors unless the user has been contacted properly.
Personally, I am 100% OK using an application that allows me to modify or delete the information it collects while I'm using it. It's when applications aren't set up to do this that I become worried and lose trust.
It's my opinion that privacy is NOT a practice conducted by public concensus, because each individual (whose privacy is in question) retains the right to feel however they like about privacy.