On the other hand, that is not the criteria for them to be successful, because they are already better on a different metric: Privacy.
I find that 90% of my queries are just "who is that person?" or "what is that thing?". Those queries can be answered by DDG just as well as Google. So I'm not giving up anything, but gaining privacy. More importantly, I'm (subtly) sending a signal to the market that I find privacy is important.
Even on the 10% of queries that are complex, DDG does "good enough". I sometimes wonder if Google has the results sorted better, but I'll gladly waste a few minutes here and there in exchange for privacy.