As others alluded to, South Korea has a strict law for mapping data, where more detailed data must be hosted domestically. The reason is probably to prevent North Korea, however ridiculous as that may seem (I guess South Korea has never heard of VPN), but probably also to protect the local businesses.
So popular navigation apps like Apple Maps and Google Maps cannot be used for driving directions, and their maps are typically far less detailed.
Of course, this should not necessarily prevent Find My network to function, but it certainly puts a damper.