Fast delivery not a daily need for most people, but the dopamine hit is huge, and it makes people buy more stuff. I think an underappreciated factor of amazon's success is how it makes normal people feel like they're the boss, who can slam their fist and get immediate action.

Personally, I feel similarly to you, that most of the time the difference between one day and 1-3 weeks shipping is negligible. However, I think that relies on certain assumptions; I buy most consumable items (food, sponges, soap, etc) in person and almost always have enough to last another month or without buying more. Not everyone does that, some are JITing their daily needs and/or don't have enough free time and energy to make sure everything is always set well in advance (think working single mom, kid needs dress shirt tomorrow for whatever).