Here is one of these safes. The first, most obvious thing is that it has a touch-screen device, a printer, a network connection, a card reader, a cash counter, and a safe. That is a lot of hardware to drive with no OS.
It also has mutliple users, with various roles for each user. Sounds like more OS stuff.
It has ways to add and delete users, and change passwords. More OS stuff.
It can make reports, so obviously it has some sort of storage, which means some sort of file system. More OS stuff.
It has ways to update the software. More OS stuff.
So the real question is, why would anyone in their right mind NOT use an OS on a device like this?