If they allowed people to back up unlimited USB drives and networks shares, /r/datahoarder would be all up their business with 1PB storage.
This is why they limit it to only stuff you're actually using.
If you want generic cloud storage with infinite retention, they have B2
What you can't do is connect a 20TB USB drive, back it up and put it in your cupboard for a year and expect the data to still be there.
/s
If they allowed people to back up unlimited USB drives and networks shares, /r/datahoarder would be all up their business with 1PB storage.
This is why they limit it to only stuff you're actually using.
If you want generic cloud storage with infinite retention, they have B2