Database activity is volatile, so they have to allocate disk space, and that takes time. So if you have light access, and then start uploading many large BLOBs,

Database activity is volatile, so they have to allocate disk space, and that takes time. So if you have light access, and then start uploading many large BLOBs, it may take time for them to allocate space, and during that time the backups might not go all the way back to X hours. And, really, all of this is just servers in a datacenter, so you can have however many 9's of reliability, and still be That Guy that wins the fail lottery.