The card vending machines are effectively rate limited, you need to wait to make a purchase. This is so one person can't empty the entire machine, even if they have multiple payment methods.
What incentive is there for the machine operators to do this?
Before the rate limiting, there were physical confrontations around the restock time. Spreading it out prevents them.
It also works better for the stores that host those machines, where they are supposed to draw in customers, if cards are randomly available throughout the day as opposed never available.
Not getting yelled at most likely. There are enough vocal people who complain if these machines do not act "fair". So it often is easier just to change how they operate and not have to listen as much of that.