Earlier quoted context omitted.
That's my main concern. Duckduckgo is used more than Bing in many countries and Microsoft might just cancel their access some day. There is always Yandex I guess
Why would Bing cancel, they're presumably making money off of the arrangement. And DDG-users would likely not migrate to Bing, but to Google: if you have to use a product by an anti-privacy-corporation, might as well use the good one.
While I do believe Google has the superior search engine, there may also be an argument for denying them the "vertical integration of identity". That is, if you use Gmail and Google Search, Google can figure out more about you (in theory) than if you use just Gmail. Same reason I never -ever- use Facebook SSO for logging into non-Facebook sites.