One of the fallacies of modern cloud and backup providers is that they actually provide a backup service. Most, including popular services like Backblaze, Mozy, Carbonite, etc contain prominent statements in their contracts that absolve them of any liability in the event of data loss. Your recoverable value in the event they lose your data is limited to either 12 months of service or is explicitly defined as nothing.
Now plenty of people pay for service with these companies, so I'm not claiming they don't make some effort to provide a genuine backup, but we're *starting* from a position where they explicitly have no liability as defined in the ToS. Now, add in the idea of storing critical or merely important files on someone else's hard drive. What happens if the drive you're storing on is a 5400 RPM Quantum Fireball from circa 1999? When that drive fails, what happens to you?
It's the same lack of guarantee with a *further* risk factor. No thanks.
When speculation has done its worst, two plus two still equals four. -- S. Johnson