In many consumer products, tests like that are often not implemented or curtailed compared to OEM products. When you buy from a company like Dell or Apple, you get the benefit of having a large organization providing accountability. In other words, when a company like Dell represents their interests in receiving quality products to uphold their reputation, they also have a shared interest with the end consumer — but carry a lot more weight since they represent large contracts with the supplier. Suppliers tend to put more effort into testing their OEM products so as not to damage their business relationships.
Anyway, this kind of thing happens all the time in consumer storage. Likely nobody was doing reliability testing on these drives in the first place since that costs money and can only expose problems they didn’t really want to know about.