I found that my delivered groceries were always more expensive than if I were able to pick out the items myself.
Obviously it will be different for everyone... but I personally dont like delivery for that reason.
Further, if I were amazon owning whole foods -- what I would focus on is minimally packaged items as a product line.
What would the impact to the overall cost of foods be if there were no need to flashy marketing/branding.
Vegetables are cheap in part because we don't need a ton of packaging and marketing around them.