With regard to your specific problem, why do you take the sticker off before you are ready to eat the piece of fruit? Wait until you are going to eat it, then take the sticker off and throw it away. This will prevent you from removing skin prematurely and will prevent the sticker from winding up with your compost. It doesn’t eliminate the stickers altogether, of course, but it’s at least a practical solution to the issues you’re having.
As for why individual pieces are labeled, it’s because the labels have the product’s produce code on them. This ensures that the produce code is always present come scanning time even if the customer is only buying a single piece of fruit. You’ll notice that there is an exception for bananas: each individual banana does not get a sticker. This is because bananas are always put under a single code and are purchased so frequently that everyone knows the code by heart (4011). Apples, on the other hand, have different codes for each variety; and peaches, nectarines, and other fruits aren’t purchased enough for cashiers to memorize their numbers.
At my local grocery store, however, there has been a decrease in what gets labeled as rolling lists that have the produce type and code listed on them have been installed at each register (including the self-service ones). So perhaps the day of the sticker is slowly coming to an end. But if there really is a law about labeling fruit, I suppose that will have to get changed first. It can’t be too stringent, however, as the banana case shows.