DDG has to show you less relevant results because they don't know much about you. The problem is that seeing less relevant search results is only considered a good thing by very privacy-sensitive people. One approach could be to advertise DDG as a search engine that works against filter bubbles and everybody sees the same results for the same query (not sure if this is actually the case).
Yes, Google also has a better index and more experience in building a search engine. I'm just arguing why DDG cannot be as good as Google, when you expect personalized results. E.g. when you are a programmer and get results for Swift the programming language rather than the pop star.
Unfortunately DDG of late has been very poor for me, and I'm not convinced it has anything to do with tracking. For example, if I'm searching for a store to buy something and the first term in the search query is my country, returning me no results at all on the first page that are stores in that country (when several such stores exist) is literally useless, and clearly DDG could have done better.
They aren't just less relevant - they are less complete. One specific example: their coverage of academic sites. As an experiment, I have entered the titles of several papers and they failed to show up in the results.
It's not just academic journal articles either: their results are, by and large, less complete - it's what initially led me to do the experiment in the first place.
