Its possible they use the delivery service to bind customers to the brand. In Germany, there are 2 major players in the supermarket business, that is REWE and EDEKA. And then there are the discounters ALDI and LIDL, but they serve a different customership, since they dont sell fresh stuff like meat or vegetables or dairy products.
In the supermarkets EDEKA is slightly in the lead - but in the delivery service they are way behind the curve. REWE instead has build up this service nicely and they seem to orientate on the Amazon principle: the customer always comes first. I was also a bit reluctant at first, as you say I also like to see first what I get. I was a bit worried they might put the stuff that soon runs out on the "best before date" in the deliveries or tricks like that. But thats not the case at all. And if something is not the way you expected, they refund you at once. The other day the driver forgot to book in the empty bottles I returned, so I didn't get my deposit back for them. So I called them a few days after, and they just refunded the 6 Euro no questions asked.
Perhaps they have spotted a way to conquer a complete new market before their nemesis EDEKA can take that over as well. And every customer who orders at REWE wont go shopping anywhere else anymore.