Those companies are growing or at worst sustaining at globally satiated production, to the best of my understanding few go hungry, technological adoption is extremely high, and homelessness and crime are low. Per-capita they keep ending off better off year over year by staying put while everything else gets cheaper. Their whole economy looks like it is contracting with the population decline but nobody is suffering a lack of supply availability to meet their demands for it. Top it off with the giant entertainment sector amount of culture they output globally and that does not ring of doomed society.
- they were an easy place to get beer before convenience stores sold alcohol or became open 24/7 (this is a bit before my time so maybe someone else can elaborate)
- a vending machine requires less space than a store.
- there is not a large difference in price buying from a vending machine or convenience store (10 yen or so).
- It is very hot in summer and very cold in winter, so people like having access to a hot or cold drink.
- a lot of people operate on a tight schedule, so their only "free time" might be when they are walking between places (home and train station, train station and work etc)
- vending machines are useful in a disaster. I believe they will give out free drinks in an emergency.
The can had a plastic lid with coins in it, returning the amount I had deposited, and the cardboard can contained an instant cold pack, presumably to assist me with managing the heat while finding another vending machine.