I am not so sure shopping carts are that great of a counter example. There are plastic ones like target, heavier duty ones, the weird ones at microcenter, lumberyard style, hand baskets, short ones, drag behinds, ones with kids car toys built in, tiny ones for kids to yeah along, ergonomic hand baskets, etc.

Then there are the innovations people had tried over the years like different styles of kid seats, calculators built into the handle, coupon scanners built in, security boots on the wheel, Aldi store coin lock connectors, motorized baskets, Ikea escalator locking wheels.

Thinking further, the designs change across the various countries I have visited over the years.

On top of this, I can visually picture all the different styles the groceries and department stores use near me to "brand" their carts and experience directly(Target's specific branded plastic carts and baskets). The very much see the shopping cart as part of their customer experience and have experimented with different setups. One could argue that the scope of utility for a shipping cart is miniscule compared to many websites. And yet, there is actually a lot of variety.

Given how there are people dedicated to so many seemingly insignificant corporate details(email signatures and other branding activities), it seems custom "website experience rules" would slot right into that line of thinking.