Because that’s what Raid 0 for, basically adding together storage space with faster reads and writes. The local backups are basically just to have earlier versions of (system) files, incrementally every hour, for reference or restoring. In case something goes wrong with the main root NVMe and a backup SSD at the same time (eg. trojan wiping everything), I still have exactly the same backups on my “workstation” (beefier server), on also a RAID 0 of 3 1 TB HDDs. And in case the house burns down or something, there are still daily full backups on Google Cloud and Hetzner.