If you're familiar with Amazon Prime delivery and use it a lot, then it's probably difficult to imagine shopping on Amazon without the service.
The ability to get items delivered so quickly, with free shipping, was a huge game changer when it debuted years ago. Sure, there's a monthly (or yearly) fee that also happens to come with music and streaming service (at least the package I'm signed up for, anyway). But it's a subscription fee many gladly pay.
Unfortunately, not everyone can afford a $100 yearly recurring charge from Amazon in one shot. And with the lack of free, two-day shipping options available, a low-income customer might be dissuaded from buying something online.