If I recall correctly, in the particular case in the blog post they *thought* they had backups but it turned out not to be the case.
But yes, as you say, tackling this issue is important for the growth of the Fediverse.
Hopefully as time goes on we will start to see the best-run instances have the best track records.
Maybe instance owners could be more strongly encouraged to detail their backup plans on their "about" page?