Big part of that is just that it's insanely easy to use compared to most of the competition.

But still, most people go to the shop to buy toilet paper. Once you get used to Amazon, it just saves so much time and effort. The prices aren't bad either, I just checked toilet paper on amazon.com and 30 rolls of good quality amazonbasics toilet paper costs $0.22 more than the equivalent kirkland product on costco.com

You can order almost everything you need in the same app, whenever you feel like it. Just a couple of clicks, no need to fill in delivery information or anything.

The only part where YMMV is receiving the parcels obviously.