I have been to Canary Wharf Tesco store countless times. The amount of times that someone scans all their stuff, pretend to press buttons, pretend to 'touch' a card to the POS, and then get their bag(s) and walk-out, and then I walk to that self-checkout point and see that ALL the items are still there and the payment was never made.. are "too damn high" to quote the meme.
And then I have to sign to a member of the staff, oblivious of just happened, and ask them to clear-up the list so I can scan my stuff. Of course the thief always speed-walks out, taking all the corners necessary to break line-of-sight so they cannot be pointed at (as someone JUST saw them walking away and can ID them easily).
Next steps, they look at their watch, wave at the cameras (I assume for retracing later who was that). I am sure that Police in London has better things to do that chasing someone stealing GBP 30 worth of groceries (which they probably do every day).
So.. yeah.. "this is why we cannot have nice things".