Primarily it's the reason you already know: restic and borg are the same model, but restic doesn't need it to be an ssh-accessible filesystem on the remote end. Restic can send backups almost anywhere, including object storage like your Backblaze B2 (that's what I use with restic, too). I agree with OP: restic is strictly better. There's no reason to use borg today; restic is a superset of its functionality.