The failure probabilities are relative. And everyone here is equivocating. As if the likelihood of failure is evenly dispersed. You indicate that storing customer data in the cloud is "playing fast and loose" but I'd argue the opposite. Not having a cloud backup is what is "fast and loose"
Imagine you are an independent bank. You need to move your customers deposits. Do you load sacks of cash into your corporate minivan or hire an armored car service? Well lets look closer. With the latter you are giving up control, right? You have no control over the quality measures an armored car service might take. Yet somehow not contracting them seems like foolishness. The reason is obvious. Its because you know in this case that transporting money isn't your expertise. Its not something you can focus adequate time and resources on perfecting. You also can't spread the risk of failure across a lot of customers, absorb that failure, and make your service better for the next go. The exact same logic applies to long term storage of data. If that isn't your only function its extremely hard to get it right.