Windows: Most use Chrome (Google default), the rest use Edge (Bing default).
MacOS: Safari (Google default) and Chrome (Google default)
Android: Chrome (Google default)
iOS: Safari (Google default)
So it looks like the only vulnerability here would be iOS and then possibly PC/MacOS if enough users switch their browser.
(and its not like Microsoft couldn't pay them either anyway)
I'm not saying DDG is amazing, only that you don't need a "Mercedes" to pick up milk.