As you said, in most cases. Mechanical (no electronics) vending machines are only possible with coins and even with electronics, sorting/recognising coins is fa

As you said, in most cases. Mechanical (no electronics) vending machines are only possible with coins and even with electronics, sorting/recognising coins is far easier than notes. A basic coin also takes more effort to forge (well enough to pass at a gas station) than a basic note, although notes seeming everywhere else but the US have obvious safety features that completely beat coins. They're also much easier to handle when you need many different ones, like when you're trying to assemble an exact amount. I can just look into my wallet and pick out the coins I need, whereas with notes, I'd have to spread them out like an awkward floppy hand of cards and especially if they weren't distinct enough scanning through and finding the right ones sounds plain annoying.