I have 2 refunds left, and I've been playing since fucking closed beta 2009.
If three chances didn't help you learn how to stop impulse buying and wasting money, getting more chances won't help. You just need to lose money until you learn.
The 3 refund system was to free up support staff from having to deal with a billion of "I bought this, now I don't want it!" emails.
Some people used it as a way to "test drive" skins. Some people used it to unlock seasonal promotional summoner icons, which became free once they refunded their purchases. Some people decided to cash in their refunds when their champ got nerfed, or when something better came along.
Whatever the case, Riot didn't care. It was their way of saying "Okay look, we've given you the tools to take care of the returns yourself, and you can do it up to three times". That's a fuck of a lot better than any other micro-transaction game would give you.