Then again, ordering something on amazon every 2-3 days already seems borderline compulsive behaviour to me too.
How often do you go to a physical store? More than twice a week? Now multiply that to cover a whole family.
I personally go to a physical store for non food items maybe once a month. My wife goes maybe once a week as she gets stuff for the house/kid which isn't easy to get online.
And I mentioned this in another reply - but a big part of it is not having to think. Let's say I make 100 orders in a year. That's $1 per order for shipping. Now, you're right, I could probably get some of those free. And there are other's I'd pay say $8 for 2 day. And yet others I'd pay $15 for overnight. You know what? If it takes even 1 minute per order to figure out which is which $100 a year is CHEAP - my time is worth a lot more than that.