100% agree. It drives me bonkers that even now with towns and cities expanding and new town centres forming, there's still a strict separation between residential and commercial use. Why not allow spaces for light commercial use in apartment buildings?
There are malls like this in the US. Such as places called "Galleria". But these seem like much more expensive projects that clearly can't be built everywhere, while the typical mall is really just an american version of an enclosed bazaar.
Also one US-specific issue is Christmas shopping, which probably drives a lot of the planing. Stores make the most money during a limited interval when they are packed to capacity and need to plan for that.
The circulation of a business's customers is regarded as a toxic impact to nearby housing. There is a decent amount of mixed zoning, actually, for businesses that rarely or never have customers visit in person.