I've always been in the "I don't get it" boat with DDG bang operators. When I last tried switching it to my default search engine, I felt like any time I needed to search DDG for "!{bang} {query}" I could have just searched Google for "{query}" and gotten the result I was looking for. In many cases, Google will give even better results for siteX than siteX's own search, because Google is likely to correct for things like common spelling errors or word substitutions.
Granted, I haven't given DDG an earnest try in a couple of years, so the DDG non-bang search results may have gotten better, but the fact that their bangs are still heavily touted as a killer feature doesn't give me much faith.