I'm curious why an ATM computer is considered secure. The general adage of "If an attacker has physical access to my machine, all bets are off," seems to not apply in this circumstance (since everyone has physical access to the machine). Why is this?
I thought of the fact that many have security cameras placed over them, but this doesn't seem sufficient to keep ATMs secure, as there is no one constantly watching the camera feed and looking for suspicious behavior. The most this could be used for is identifying an attacker after an attack has been attempted. It seems like this is fairly easily solved through plain clothes, a mask, gloves, etc.
So if this alone isn't or shouldn't be enough of a deterrent, why do we not see ATMs getting hacked for all their cash at 4:00am? What makes the device so secure? Is it just a simple risk-reward analysis, where the cash in the ATM isn't worth the effort of the hack? Or is there more to it which makes the computer secure?
Also, I noted that there have been a couple questions about ATM security (like this one and this one), but mine is about the physical security of the machine, since it violates a common security principle, not anything network related.