How many loyalty cards do you have? Imagine how many you'd have if you had one for every shop you'd bought something from. You'd need a card wallet that reaches the floor!
We've all been there. You buy something in a shop and the cashier offers you a loyalty card and you accept it because it sounds like it'll be worth having. But once you sign up, you'll receive unwanted emails, you'll have to carry it around everywhere and it takes up extra space in your purse/wallet...