I think you underestimate how many Americans just want a cup of Joe with cream and sugar. A whole lot of us are out there drinking gas station/convenience store coffee or brewing a cup or pot every day of store brand pre-ground.

And the ongoing joke about people getting frustrated with just wanting a “large coffee” and being confused by starbucks calling it a “venti” and spouting off about how they don’t want any fru-fru mocha-chino late bullshit even though no one asked.

I think the bigger issue is that of how Americans get around and how available real estate is.

Japan has a lot more people who can/will walk, take the train, etc. that’s a lot more opportunities for them to walk by a vending machine.

Americans tend to get around in our cars, so if you want to sell them a coffee, snacks, hot meal, etc. they need to be able to park somewhere.

And vending machine food isn’t exactly a huge draw, people probably aren’t going to go to your parking lot with a row of vending machines just to grab something to eat, so you kind of need something else to draw them in, some bathrooms, gas pumps, or at least convenient parking to other stuff they need to get to, so you might as well stick a gas station there, and since you’re going to need a cashier you might as well move that vending inside and you can get more and more variety of merchandise on shelves that you can cram into some vending machines so it might as well just be a convenience store.