The people who made your car were legally required to test your model of car by crashing it into another one and making sure the airbags work. This is also too expensive to test yourself. One does not modify an airbag system at all without retesting it.

Your hosting provider has no legal requirement to test their backup system. At best, they have a contractual obligation. And they don't know how to test recovering your site, because testing whether it works is a different process for each site. Additionally, it's cheap to test backup procedures. Most people have a spare computer somewhere (maybe not in the data center), and it should only take a few hours to restore a copy of your site. Once a year. For Chris's sake, you could probably do it in the background and put a movie on.