[illiac786]

The answer to your question is in the comment you replied to.

How would you sync between devices without internet except if they are on the same network? Good luck with sharing passwords with family members...

[sshine]

It is a common problem today that in order to transfer data between devices located in the same room, it needs to pass by a data centre on another continent.

Instead of internet you use local transfer networks, e.g. WiFi, Bluetooth, LoRa, RFID, QR codes, USB, etc.