Technically it's in the European Economic Area (EEA) but the title was too long.
E.g. EU enforces free data roaming for cellphone providers, but many providers allow free roaming to Switzerland and the Nordic countries too - not sure if it's just practically easier than trying to geofence those areas into a different tariff or if it's legally too complicated, but I'm fairly certain they don't do it out of the goodness of their hearts.
See also https://en.wikipedia.org/wiki/Template:Supranational_Europea...
No big mystery: because EEA countries agreed to the ruling to make that a requirement and not just EU countries?
There is tons of stuff applicable at the EEA level, it's quite common. After all the purpose of EEA is to have common regulatory framework.