DDG gets its results from other search engines. Bing is one of them.

There was also a big thing about DDG allegedly selling user data to Microsoft, which the living brain donors of 4chan probably interpreted as DDG being a different front-end to Bing.

My understanding is that they outsource the search part to bing's search back-end. Saying DDG is just Bing is like saying two butchers are the same because they get their meat from the same supplier.

There are really only two usable search engines actually indexing the entire Internet: Google and Bing. Yandex also does but I've never seen it recommended for anything other than Russian language content (the company itself seems to be falling down a mineshaft at the moment). Baidu also does some although every Chinese exchange student I talked to about it (admittedly not many) advised only using it when Google is blocked. Every other engine is just wrapping Google or Bing (yes that includes Yahoo and DDG)

This is the kind of ugly truth of the search engine business. It's a duopoly at least in part because the indicies are expensive to scrape, build, and run. You need to continuously run a large number of servers loading web pages and often running scripts. You need to be large enough to negotiate with content providers not to block you. Keep in mind paying them may bankrupt you as your margins will be thin. Google has a huge advantage here they own a good chunk of the online advertising industry and can afford to throw money around in a way a search only company wouldn't be able to (this is why the European and Canadian link tax schemes ironically cement the existing monopolies). You need to continuously run large linear aglebra transforms on the results (PageRank is expensive). You need to store all your indicies on large expensive servers with a lot of memory as hitting disk may take too long. Results need to be fast and you will make next to nothing on each search.

Nobody else has mentioned this but there have been several times that Bing censored something and it propagated to DDG, most notably when Microsoft censored Tank Man (intended for China, probably) but then Tank Man also was censored on DDG.

Partly because of these incidents, I could never consider DDG reliable.