[jjeaff]

How do you know? As I said in my comment, they may be drives that didn't quite meet the qc threshold.

All drives usually ship with a certain number of bad sectors. An excessively high number of bad sectors can mean there are quality issues with that specific drive. They may be 'binning' those more poorly testing drives for the external USB drives.

https://en.wikipedia.org/wiki/Product_binning