At least here, there are randomly triggered checks by shop staff where they have to manually rescan anything before they let you leave. And possibly, those checks are more easily triggered if you do certain very strange things like buying nothing but many separate instances of "bananas' with widely varying weights. Wouldn't be too hard to program a set of rules for the most obvious red flags.

And of course, the area is wide open and well covered by cameras, and usually self-checkout means paying by card or google pay or something, which will tie your identity to the purchase.