[vineetmarkan]

Because blockchains are great for exchange of value/transactions. Tokens can be easily transferred and hard to re-create and safe. They can be re-generated after each transaction and stored in a wallet.

Associating one QR code with one shoe is simply not the same thing. Nike doesn't have to make the whole ledger public through give the nature of blockchain, it can be assured that it has not been altered.

[AstralStorm]

They don't have to with QR codes either, unless you're willing to enumerate all possible codes in their verifier.

Also the thing is not stopping anyone from providing a wrong code. Unless every transaction concerning their shoes is recorded on the block chain, which it won't, and which brings privacy issues.