It is not about whether a cloud provider has the necessary failure prevention techniques. This is about sovereignity over your own data.

If you store your data in a cloud, and it is not your cloud, then the owner of that cloud can cut off your access to this data at any time. With the usual contracts, your means to counter such moves are moot at best.

Having important data in your own hands is vital. I do not put data on the net that i cannot afford to lose - either, I don't care (e.g. like the contents of this post, if it gets deleted, I'm not hurt), or I do have the data here, in my own home, on my own servers, on my own backups.