most grocery stores have a number system so that a cashier can punch in a number to ring up a certain product. this is especially useful for fruit and vegetables, as often times it doesn’t have packaging and doesn’t have a barcode. the vast majority of groceries use 4011 as the number for bananas.
I’d imagine it’s because the number 4011 is already used in production and logistics of bananas, so the grocery stores just stick to the barcode/number that bananas already have on their box when they get delivered. that’s just a guess though.