3-2-1 rule - why is the onsite backup typically the primary backup, not the offsite one?
So I understand the 3-2-1 rule and the need for offsite and offline backups – however, I don't understand why most seem to suggest that for the average user the offsite backup typically is the offline backup, ie secondary backup, and not the primary one?
We're currently implementing a setup where the primary backup is a NAS placed in a family home far away (connected via tailscale), and the secondary backup is a cheap convential HDD lying around ('in cold storage') somewhere in our home and only connected periodically for manual backups.
Why wouldn't this be the most time- and cost-efficient setup for the average user?
(Additional context: The data we're talking about is primarily ~4 TB of family photos, I'm aware the considerations change based on the exact use case)