My understanding is that it’s not a “low quality” issue for external drives it’s a “low quality control” issue. A lot of the best prices for electronics come from companies who spend less on quality control. That means most of the products produced are going to be just fine and a steal for the price. But, there are going to be a higher number of lemons that end up sold. Some of those lemons won’t be revealed until after the warranty has expired. For external drives, they take drives from their other lines which come from batches which don’t test out as well in their quality control. That means most of those drives are just fine and as good as their higher priced versions sold as enterprise drives. But, you take the risk that you will get one of the lemons and it may not be simply dead on arrival but have issues that appear over time. Again, it’s not that the drives that get put into the external enclosures are some separate low-quality line produced specifically for external enclosures. They are drives taken from their other lines that come from batches (i.e., they didn’t test each specific drive, it’s a failure rate across a batch of drives) that didn’t test as well in the quality control process as the ones that end up being branded and sold at higher prices.