I composed the story that Walmart should create their own cryptocurrency just to ... catch your eyes  

In fact, they do not need. Yes. You are right. They do not need it. They can take directly Bitcoin as the bonus for their customers.

But you can think of this further than just Walmart and the bonus given to customers. Walmart do not need that kind of bonus. People will also not be attracted to Walmart just because they give Bitcoin. It is better they give them cash or discount points. So Bitcoin is not the point. A new coin, which needs to be introduced, is the point.

Imagine Walmart is our cryptocurrency community. Among us, cryptocurrencies are accepted. But out of this community, people still do not know anything about cryptocurrencies. They also doubt of them. They think of Bitcoin, Ripple, Ethereum, and cryptocurrencies in general as "virtual money", Ponzi schemes, scams ...

Unless you give the cryptocurrencies to their hand, you will never persuade them quickly enough to make them learn and accept cryptocurrencies. But how to give them a cryptocurrency ? They do not have an wallet for you to send. And if they do have wallets, they are not the targeted people for us to introduce cryptocurrencies.

Giftdrop paper wallet can solve this problem first. Besides, giftdrop paper wallets have many other applications. The story of Walmart above is just an example case in suppose.

Paper wallets are the physical form of cryptocurrencies. Let's think of utilization of this mediums.