Under what conditions can I be a citizen of a country  but do not have the right to live there?

The question arose while reading the [VWP conditions][1] for a travel in the USA... where suddenly I've found this (emphasis mine):

> To be eligible to travel under the VWP, **British citizens must have the**
> **unrestricted right of permanent abode in** England, Scotland, Wales,
> Northern Ireland, the Channel Islands, and the Isle of Man

Therefore the question.


  [1]: https://travel.state.gov/content/visas/en/visit/visa-waiver-program.html