The Expectation of Free Shipping

Free Shipping Isn’t Really Free - The Atlantic

In a 2018 survey by Internet Retailer, shipping charges were cited as the most common reason shoppers abandon their carts, topping the pet-peeve list for nearly a third of respondents, ahead of things like not wanting to create an account and being unsure of the store’s return policy.

And:

In general, Dhar says, shoppers are even willing to pay more overall for the same goods if there isn’t a separate shipping charge.

This article is full of good stuff, and I definitely found myself nodding along, thinking “yeah, I would totally rather buy $10 more to get something I don't need than pay $5 for shipping.” It's not rational, but it definitely resonates.