This might generate more buyer friction[1]. Grabbing an item from a shelf is very easily reversible. But when you push a button for a vending machine to dispens

This might generate more buyer friction[1]. Grabbing an item from a shelf is very easily reversible. But when you push a button for a vending machine to dispense something, it's not obvious how to undo that. So you will hesitate more. Also, when people change their minds about buying something, stores need to re-shelve that product. That's probably more labor intensive for vending machines than for regular shelves. For that matter, stocking it in the first place is probably more labor intensive. --- [1] Every obstacle you encounter, even a tiny inconvenience, will reduce the odds that you go through with a purchase.