You can't copyright the GPS coordinates of cities, because those are facts. The data would be the same whether you compiled it or not, and it would be absurd to grant someone a monopoly on that data.
If you compile a word list yourself, you've created something that doesn't describe the factual state of the world; you've created something new.
FWIW, before the debacle, even the (apparent) author of it appears to have admitted that it flaunted copyright:
> FWIW, I have reverse-engineered the what3words address decoding algorithm. If anyone else with the luxury of flaunting patents and copyrights is curious, check out the demo at https://cardinalhood.github.io/what3words/. It’s written in JS, and runs in browsers and Node.js.
Whether or not a collection of facts can be subject to copyright varies across jurisdiction - in the US you can't copyright the phone book, while the EU has a specific concept of database rights. What's critical in the US case is whether there's any creative expression in the collection of facts or whether it's effectively mechanical, and whether the w3w wordlist would be protected under that would seem like an interesting case.
If you compile a word list yourself, you've created something that doesn't describe the factual state of the world; you've created something new.
FWIW, before the debacle, even the (apparent) author of it appears to have admitted that it flaunted copyright:
> FWIW, I have reverse-engineered the what3words address decoding algorithm. If anyone else with the luxury of flaunting patents and copyrights is curious, check out the demo at https://cardinalhood.github.io/what3words/. It’s written in JS, and runs in browsers and Node.js.
https://blog.ldodds.com/2016/06/14/what-3-words-jog-on-mate/