I'm entirely guessing, but the cost of warranty/support might be a factor too. If you buy an external drive in an enclosure, and mess up the removal-from-case

I'm entirely guessing, but the cost of warranty/support might be a factor too. If you buy an external drive in an enclosure, and mess up the removal-from-case and subsequent actual install, it's much easier to refuse obligations as the device was "misused". A bare drive sold to a private consumer probably has way more installation problems than anything else in this market. (Again: guessing.)