I once bought a secondhand PC and the previous owner hadn't even bothered logging out. I booted right into Windows and had full access to everything. I tracked them down on LinkedIn to try to prevent that from occurring in the future and they wouldn't respond.
They were probably freaked out.
There's no way in hell I wouldn't dismantle my HDDs to play with the pretty mirror disks/magnets inside.. but.. let's say I messed up and didn't keep my precious mirror disks..
I would not respond to some random person that contacted me through LinkedIn to give me a lecture about my HDD data habits.
Maybe they didn't respond because they were.... dead? And their pc was just sold off by relatives or the estate?
(Unless you did purchase from them directly.)
I once bought a copy of the book Cosmos by Carl Sagan on eBay. Tucked away inside was a very interesting letter from a woman to the owner. She had given the book to this person as a gift, and reading between the lines of the letter it really seemed like they had some kind of love affair. I found the letter quite touching and was fascinated by it. I emailed the ebay seller, trying to find out a bit more info or if the letter was important to someone - but it turns out the seller had just picked it up at an estate auction. Apparently the owner had passed away. So a book about the Cosmos, that was once a token of potentially forbidden love between two people, was now in the hands of a stranger. I felt a bit of profound sadness knowing that no one else in the world probably knew or cared about this significance. I still keep that letter in the book to this day. It seems fitting.
Though, that sort of romanticism aside, if I were in your shoes I would just totally format those drives and not dig too deep to see what's on them. Just my luck, it would be a bunch of **** pics or something.