I agree, but time is money, and it's much quicker to flatten a drive than to hook it up to a box and wait for it to do several erase passes. I do remember seeing demagnetizers though, and I'd assume they'd also work just as well.
It would only take a few seconds to unscrew the cages. Those suckers get expensive when you're replacing them with every new drive change.
It's quicker to just replace the tray with a new one then swap it. If one of us wanted to take some of them off in out spare time to keep for personal use we could but no one ever bothers.
Not sure if either of you have ever worked in the health care industry before but because of the HIPAA and HI-TECH acts we have to actually destroy all devices taken out of production, whether its because they are broken or being upgraded, replaced, etc. Even keyboards have to be destroyed. Crazy, I know.