It's an abbreviation of Duck, Duck, Goose. They don't really explain why they chose to name it after that game.

https://duck.co/help/company/name

Maybe it's their ranking algorithm.

DDG is an anonymized wrapper for Bing.

Wikipedia provides

Weinberg explained the beginnings of the name with respect to the children's game duck, duck, goose. He said of the origin of the name: "Really it just popped in my head one day and I just liked it. It is certainly influenced/derived from duck duck goose, but other than that there is no relation, e.g., a metaphor."

My guess would be from the child's game "duck duck goose".

Maybe the creator really enjoyed that game as kid!