I believe it might be because DDG is not Google. What works on google might not work the same in DDG.

How long have you been using google? Probably long time. During this time you (unconsiously) learned how to ask questions "google way", now you need to learn to quack :p

I also found that DDG sometimes (not very often) does not find what I am looking for. Mostly it is because I know nothing of the subject ie. using a description of a "thing" I am looking for instead of its name, etc. - theese are the things google is better at.

Regardless, if you find such query than please submit it to ddg, they are very responsive and results do get better.