Regardless of theory, pay attention to where cameras in corner shops are pointed and I think you'll see what I've often seen: the cameras are primarily positioned to watch employees.
The only way to know who is stealing is to either watch the drawer or to count the cash every time the employee walks away. Of course, most places go with the former as the latter is too time intensive (especially during a rush). The better solution (IMO) is to just count at the end of the day, and if there’s a discrepancy, mark it down. If it happens multiple times, you can compare who was at that register for each of those days and narrow it down.
At least in the grocery stores I frequent (Bay Area), the employee takes the drawer with them when they walk away (usually shift change) - clearly another option. I think they sign in/out too, so the drawer and the transactions are connected.
Street crime is generally not committed by people accurately evaluating their options and making optimal choices with a long-term view.