That was during the flooding in Thailand that took out a huge chunk of hard drive manufacturing capacity. Electronics stores started putting quotas on purchases, so BB offered a bounty to friends and family who would bring in hard drives.

They had a disassembly line gutting external hard drive enclosures for the hard drives, too. One of the drives in my array was acquired via a similar process.

You should read the whole story. I should probably read it again myself.

https://www.backblaze.com/blog/backblaze_drive_farming/