I think it has to do with available space, as other commenters have mentioned. Here in Valencia, Spain, there's a huge amount of unused "retail" space. Most of the city is 5-7 floor apartment buildings with the ground floor being designed for retail / parking / etc. There are many building, outside of the city center that were built years ago with their ground floors sitting empty since day 1. Many spots that were occupied at some point are sitting empty as well. It's pretty cheap to buy or lease a space. Anyways, in the last 5 years or so there has been a lot of spots being converted into vending machine spots. Basically a small area of retail space, no front door or wall, and maybe 4 or more vending machines in it. I've noticed sometimes even some cafes are carving out a little spot of their frontage to install a few machines.
