Here you are wrong too.
If you want to develop an app via an API that is only offered B2B, what do you do ?
Yes, that's right ...
You phone up REWE and negotiate a license to access to the B2B API to develop your application. B2B2C if you want to put it in simpler terms.
My original point stands. REWE clearly do not want to officially expose the API B2C, almost certainly for the exact reasons I already spelled out in my original post.
But no, its easier for you just to spread FUD, claiming "busines has no interest in providing more price transparency to their customers" just because they will not let you have access to the API as direct B2C.