For me there are two key aspects, backup shelflife and multiple multi-site backup.
I've seen a few cases in my time where really bizarre things happen. In one case, a coworker was migrating his PC-XT files to a new PC-AT using the provided floppy disks. What he didn't realize was that these disks were specifically for the PC-AT drive and required a higher write current to record data properly.
He dutifully backed up his files to these disks and formatted the PC-XT harddisk before beginning his transfer to the new PC-AT. Incredulity, panic and then horror set in as he discovered that there was nothing saved on the floppy disks.
I've seen similar issues where someone was in the wrong directory or used an unfamiliar script that deleted all files on the harddisk because an argument ie subdirectory or filename was missing and a command like: DEL c:\ was run or in my own case rm -rf /bin on a unix box.
I've seen casette tapes get mangled in the recorder (cassette tape was popular with early PCs like the TRS80, Sinclair...)
I've seen CDs get mangled when placed in the CD drive too quickly with the door catching it at the wrong angle. I've seen floppy get demagnetized because your kid ran a strong magnet (the infamous superduper red horseshoe magnet) over the floppy to see if it could pick it up.
I've seen static discharge accidentally take out a USB stick at the wrong moment.
In the end, it seems that external USB drives are best. They carry their own R/W hardware, are heavily tested, can be copied at a fairly high rate and are more flexible than digital tape ie directory/file retrieval.
You can run diagnostics on them to insure files are still good. As long as USB is around, they should still be readable. Other media like CDs, DVDs, BluRay... require the appropriate hardware to read/write them and will fall out of use like the floppy disks did before them. You can have multiple external drives connected at the same time for camparison tests...
There are ways you can use external drives to do partial backups to limit the number that you keep around with some being sent to offsite storage in a bank vault or other safe places.
Here's some tape (works for external drives too) rotation strategies to consider if you're serious about backup management.
https://www.recordnations.com/articles/tape-rotation-2/