I’d put durability and longevity at the top of the list of advantages for tape backup. Personally, I think some of the durability figures for other types of backup are overly conservative and rather short, especially with SSDs. But better safe than sorry, I suppose.
Another advantage of tape is speed. You can expect 500MB/s or more with tape, versus maybe a quarter of that with a HDD. Yes, tape backup is linear, which has positives and negatives, but for now I'd still put speed as an advantage for tape.