I live within the city limits of Lexington, Kentucky, which is a mid-size town of over 300,000 residents (and incidentally, a fairly progressive "blue island" in this very red state), home of the University of Kentucky. There are three Amazon warehouses / distribution centers each less than 15 miles from me, all about a 20-minute drive away. On some purchases they offer me free next-day delivery.
My theory about the coupon eligibility, as I alluded to earlier, is that they offer it to customers that they think can be lured into spending more money with them. Ironically, I might throw too much revenue their way to get a break! But really it's a giant black box, and I bet there aren't even that many Amazon employees who understand their algorithms. Maybe none, if they're using pure AI.
Apologies to any followers of this thread that aren't interested in this somewhat off-topic side discussion...