[swombat]

I suspect the reasons are to do with practicality and dealing with customers who mistakenly cancel, rather than any kind of malice.

E.g. if you keep backups of deleted files for 30 days, the files are technically still within the service's reach, but they won't look at them unless you ask them.

Ultimately, if you want your files to be completely secure, and you really care that when they're deleted, they're permanently deleted, you probably shouldn't trust any third party backup service anyway. Even if they do delete the files, they could easily be recovered by forensics examination of the hard drives.