Your first sentence hit the nail on the head. Most Americans travel nearly exclusively in their car. Why would they get out of their car to use a vending machine when McDonald’s has a drive-thru? Or if they are willing to get out, why wouldn’t they just pick up fresher food from a restaurant? Moreover, mobile ordering has solved the issue of having to talk to people.

The US does have some vending machines like this, but pretty much exclusively in areas with very high foot traffic, like airports, train stations in major cities, etc.