One of the slightly subtle advantages of disk-based backup systems over tape-based backup systems is that capacity expansion is much easier; all you have to do is start using bigger disks. Since SATA is SATA, you don't need to replace your enclosure, and it is relatively easy to have multiple generations of disks with different capacities cycling through your system.

Contrast this with tape backups. To upgrade to higher capacity tapes, you have to not just buy the tapes, you generally have to buy an entire new tape drive that can write the new high-capacity format, for much more money and often a much more complex environment (at least in the old days, new tape drives were often not truly happy writing to the old, lower-capacity tapes you already had, and sometimes couldn't do it at all).

Fundamentally, what's going on here is that tape has a made a tradeoff; it has put the work and the smarts in the tape drive instead of the media, so that the media is cheap and simple while the tape drive is expensive and complex. Modern hard drives have gone the other way; the hard drive is ferociously complex (and is only cheap because they are made in such bulk), while the interface is relatively simple and general.

(There are subtle advantages to the tape tradeoff; for example, the simplicity means that there is less to get broken in tape media. And the tradeoff is a great deal if you have a lot of tapes compared to how many tape drives you have.)