Google has 90% market share. DDG has 0.7%. I don't have a POV on whether AI mode is good or not, but surely there's gonna be some people who dislike it, and even if that's a tiny percentage, it can be a huge boost to DDG.

0.7% * 1.28 = 0.9% market share today.

A large fraction of the people using Google probably have no idea DDG exists. So the backlash is likely significantly larger than just the 0.2% who left to this search engine.