Vending Machine (自動販売機)

Vending machines are part of the Japanese landscape. You will find it everywhere, so as long as you have some coins, impossible to do not find drinks.
In summer, only fresh beverages are available, but in colder seasons, you can find hot drink (coffee, coffee milk, milk tea, tea, cocoa…). They are always distinguished by colors: cold beverage in blue, hot in red (see picture above).
When some friends came to Japan for the first time, they were so surprised by the quantity of vending machines in the same street. I get used to it but that's true that it is not rare to see several machines at only few meters apart. If I take the example of the street where I live, on 150m, there are 9 Vending machines, so a vending machine every 16 meters. I am wondering the reason or the necessity of so many machines in the same area.
I have talked about it with some colleagues, and they were joking : “this is useful, see, at night this make the street brighter!”.
H.