One large difficulty is that most backups are stored but not checked. One place I heard of had special machines that did nothing but run restored backups! If your data was encrypted when stored, the runs from backup would show that pretty quick! Of course, the OS build on the checking machine is pristine.
There had been a place that religiously did backups. Then, when they needed one, they found out the tape drive they used did not write!
I have said "Work, like matter/energy, is conserved. It tales so much work - the variable is who does it!" And what the costs are if not accomplished.