I’ve noticed this too. Not only what you stated, but how the search terms aren’t always respected; ie they do similar terms, even if the term or phrase is in quotes (the quotes should mean exact matches only). They also do a lot of filtering of the results if they feel I shouldn’t be seeing them. I can take my same search query from DDG to Google and most of the time find what I’m looking for.
If I understand DDG correctly, they use Microsoft Bing as their backend for search results. So while they may be branded DDG, the results are in fact out of DDG’a control. It also means we are more subject to Microsoft’s privacy policy than we are to DDG’s.
I’ve been wanting to move away from DDG because of these reasons, but have been unable to find good alternatives. Hopefully someone here can make good suggestions.