Sure, but you also aren't paying super close attention to the DDR cab either if you're in line. You're looking at things around the arcade and maybe pacing around a bit so that you aren't just hovering over the other people playing.
Not only that, but losing a toonie is absolutely not the same as losing $50 on a card. It's an entirely different scale. $50 is far more attractive than $2 to a potential thief
Also, where were you that the machine took toonies? Every arcade I've been in was loonies until they switched to the cards.