Can you provide source of the claim that DDG search is 'outsourcing the search infrastructure Bing'? This appears to be a regular claim, but as far as I know, DDG buys search data from multiple parties, including Bing, Yandex, and many others. They have their own web crawler as well.
Because outside of Russia's Yandex that works well only in Russia and China's Baidu that works well in China, there's no other alternative. That "etc" in your sentence is not an "et cetera".
Bing is the only game in town for Google alternatives.
If you look at the info page by DDG cited in Wikipedia, it'S over 400 sources for the "instant answers" section, not the normal search results, and the phrasing is at least unclear if their own crawler contributes to the normal search results. https://duck.co/help/results/sources
