DDG also uses Bing. I've never used Ecosia before, but it's interesting to me that the experience would be so dramatically different when they're both using the same source. Must be some interesting factors involved in DDG's search to assist in pulling more relevant results out of Bing.
DDG isn't just a skin over bing. I heard it consumes multiple sources and applies its own ordering rules.
I do not know about Ecosia, but DDG does not use only Bing. According to Wikipedia, it uses over 400 different sources. So in theory, given they have a smart enough algorithm, DDG should be able to produce better results than Bing.
Pretty sure the search results are from Bing, while those other 399 sources are for other things, like quick answers, dictionaries, translations, currency conversion, flight search, etc.
It's Bing. I've noticed the slightly lower quality.
It's something of a conscious choice: unfettered tracking and advertising practices but good search results, or less tracking and OK results with profits used for a cause.