I think they are aware of what you're suggesting they wrote:

"Then again, knowing the humble size of our userbase, we should let neither our expectations nor our imagination run wild on this front."

Still it is the first browser which chooses DDG as its default search engine that I am aware of. This is quite a thing for such a small company like DDG. Now others can follow (or not) when they see that it worked (or not) for Gnome. And even if on Linux more people are aware of the fact that they can change their search engine in the browser, still there is a fair amount who just use what is there. It is therefore browsers nowadays are developed, do sell the default search engine position.

I remember the days when IE had 98% of the market share.