unlike other sites like DDG actually has its own crawler whereas most alternatives are just frontends for google/bing
Just so you know, DDG does have its own webcrawler (DuckDuckBot). It takes results from that, and the Bing API, and other sources, to generate results.
Also, they pay Bing for results from the Bing API (which as I understand it gives configurable access to the Bing index) and so even the results that do come out of Bing are quite different than you’d get compared to just a “frontend for Bing”.
I always get confused by this analogy because my mind goes to beer representing open source (the ingredients aren’t secret, and you can brew it yourself if you want to). “Free Coca-cola” would work better, like you’re not paying for it right now but only one company knows how to make it.