"Wikipedia for structured data" seems like an odd tagline when Wikipedia already has a Wikipedia for structured data.
That said - the explanation didn't fit as well into a one liner :)
For example, in the cryptocurrency space. Projects raise funding through initial coin offers (ICOs). In an ICO, you can contribute ETH to a smart contract for the promise of tokens in the future. Having an openly editable list of ICOs and their contribution address would not work. The list would be quickly spammed because malicious actors have a really high incentive to put their personal wallet address as the contribution address.