If there isn't a vending machine offering healthy stuff, the reason is there isn't a profit in it - either people don't buy the product or it costs so much to stock, that even if they do, it doesn't make financial sense.
As I said earlier, one of my two local hospitals had a hot pasty/pie/sausage roll mahcine, they also had a sandwich machine - which offered sandwiches of the worst dried up curly breaded kind, at a higher cost than the hot pies/sausage rolls...
Thats now gone, replaced with a chocolate/crisps machine. The hot pies are as popular as they ever were and really smell pretty rancid.
The sandwiches did include cheese and onion, tuna and egg, all of which smelt pretty bad.
Vending machines are supplied by businesses who rent space to put them wherever they are, they need restocking and emptying of cash often. If they don't make money, they don't cover the rent/outgoings, just like any other business.