Staff member watches theft happen and let's it be

I done some shopping at checkers and after paying and leaving the trolley which is not allowed out the shop .I forgot my bag of clothing items in it .not realising as I walk off and neither getting any signal from the cashier that I forgot the bag there ,I walked off and not even out of checkers properly and I turn back after realising I forgot it there ,I go and ask the cashier and she has the oddasety to tell me she did see me leave it there and saw the customer behind me in the queue take it and walk off .my question is ?why didn't she call me back when seeing me walk off without it .and why did she not report the theft to the manager or security on duty.I'M SURE IT'S ALSO OKAY IF WE ALL JUST RANDOMLY WALKS OUT WITH OUT GROCERIES WITHOUT PAYING .STAFF WILL JUST WATCH.