The example of same/next day delivery doesn't suggest anything special about Amazon though. It's really just an argument of economies of scale.
A small business usually only addresses a very specialized part of the market so they don't really ship that much stuff and thus can't hire that many people to deal with shipping without a huge overhead. However, if you stack thousands of businesses onto a marketplace, and then handle logistics for all of them, now there's much less overhead: the same shipment can combine many different specialized things.
Also fwiw Amazon is by far not a pioneer of fast delivery. Same day delivery has been around in densely poplated places (like in China) years before Amazon even started trialing the service.
Sorry mate, but I'm going to call bullshit on this. I've grown a home-based eCommerce business from nothing to 400k sales a year with 5000+ active SKUs.
Once you've hit around 5-10 sales per day, there is absolutely nothing physically stopping anyone from doing same-day delivery apart from poor inventory management or a simple unwillingness to do so (which is valid; some people can't work every day due to family commitments).
You have provided evidence for the exact same point I'm making, economies of scale. You have a large ecommerce business with a variety of things to sell so you benefit from economies of scale in shipping.
Most small individual sellers have maybe like 50 SKUs which makes it prohibitively expensive to do same day delivery.
No, I think you've missed the point. 5000+ SKUs make the logistics _harder_, not easier.
Back when we only had a couple of dozen SKUs, it was much easier to get everything out same day. Package them all in the same envelope, stick in a red post box. Done.
It doesn't make logistics easier, but it makes it worth investing resources into. Economies of scale means you get more value for the resources you do invest into logistics.
Anecdotally, almost all small online businesses I've seen the back end of do not have a dedicated logistics person. When there's only a handful of different kinds of stuff to ship, shipping becomes an extra low-skill task usually given to whoever is free. They also usually do not have a sophisticated inventory management system (because it is not worth it to purchase one), and instead use spreadsheets that are manually managed.
Secondly, sending out stuff same-day is not even close to same-day _delivery_. For that you need to control all aspects of the logistics chain, which only makes sense at Amazon scales. I've encountered many times where I've ordered things, had a label created the same day but then with no progress for a week. After contacting the seller, it turned out the courier only picks up packages from their warehouse once every 3 days, and then takes another couple of days to "ingest" it and do the origin scan.
A small business usually only addresses a very specialized part of the market so they don't really ship that much stuff and thus can't hire that many people to deal with shipping without a huge overhead. However, if you stack thousands of businesses onto a marketplace, and then handle logistics for all of them, now there's much less overhead: the same shipment can combine many different specialized things.
Also fwiw Amazon is by far not a pioneer of fast delivery. Same day delivery has been around in densely poplated places (like in China) years before Amazon even started trialing the service.