This isn't really any different than StartPage. What I find a good search-flow is that instead of doing a !g [search] I just use !sp [search], instead. That way you don't land on Google for the search at all but you get the entire list of results and StartPage has a better stance on privacy.

Regarding DDG on general, I've been using it exclusively as my first search provider and it has ramped in quality searches at a nice clip. I find myself bouncing through to the above search-flow less and less over time and I'm now in the process of deGoogling other things.

Keep donating to those privacy focused services where you can! DDG is a prime example of showing how these services can exist without an agenda, other than customer oriented features.

Because it's traffic they can serve ads to. Why wouldn't they? It's 100% win for them. They're getting someone who is dissatisfied with another search engine to try and win them over

Well, it just redirects you to google, so google can serve you ads etc

A better question is why they allow startpage.com (a.k.a. !s). I think at this point, fighting scrapers is just not worth it. But I predict one day someone is going to write a client-side desktop app that scrapes all this stuff and presents it AOL-style, it'll get popular, and all the sites will freak.

All of the bang commands are probably a great way for them to get feedback on what they're not giving good results from. Very targeted training data.