Large scale NAT is one reason that would fail. Some mobile carriers have most of their customers behind a handful of IPs. Wikipedia has dealt with this a lot, a

Large scale NAT is one reason that would fail. Some mobile carriers have most of their customers behind a handful of IPs. Wikipedia has dealt with this a lot, and has a page explaining why conflating an IP address to a person isn't usually the way to go. https://en.wikipedia.org/wiki/Wikipedia:IP_addresses_are_not_people https://en.wikipedia.org/wiki/Wikipedia:IP_addresses_are_not...