I get what you're saying, but here's my mindset. Walmart has a subscription service with free 2-day shipping (I get it's not free, but stay with me). They also have Jet which does the same thing. They aren't going to beat Amazon by playing the same game, so why don't they take the next step forward? It wasn't logistically possible when Amazon started doing it, but they figured it out.

And it wouldn't be logistically possible for most others starting out, either. Amazon has built out the capability over time, and I believe it now includes its own planes, trucks, warehouses and delivery staff.

I agree that promising and delivering on universal 1-day shipping may be one of the last ways to differentiate an online offering, but it either requires loosing a lot of money on individual sales or significant capital to build out the logistics/infrastructure yourself and hope the customers follow.

Amazon has free same day delivery on a huge selection of items in my area. They also have free One day shipping on almost everything here in San Diego once you order $35 worth of items

They will do same day shipping within a regional walmart / target. It'll probably end up an instacart like service.