Yeah, I know about bangs, but on mobile they are cumbersome to use: I have to tap my screen 7 times to change from DDG to Google:
1. tap DDG search bar
2. tap space
3. tap shift key
4. tap "!"
5. tap shift key
6. tap "g"
7. tap enter key
If DDG included a simple button, it would be 1 tap. Of course, I can't blame them for not linking to Google, but this way I will stick with Google.
[1]: https://duckduckgo.com/bang