I am suspicious that those machines wouldn’t be cleaned properly
You are right to be suspicious.
In order to maintain hygiene properly, the machine has to be powered down, the contents drained and discarded, the machine then cleaned by hand, refilled, powered up, and then it takes a while to start producing crystals again.
It's enormously time consuming and eats into their profitability, managers hate them because it's a drain on manpower, and there's no guarantee the staff doing the job give it the necessary care and attention anyway. Most of the time it's a simple case of filling up the syrups as and when needed, and paying them little heed otherwise.