I'm sad Bookdepository is closing.

Notice they don’t make independent or sell it to management, they kill it.

How many buyers are there for a company in a declining niche that did a $6m loss? Is it worth anyone's time?

If it had a significant customer base, lots. There are lots of 'turn around' experts out there.

Most of the tech companies people on this site work for are making a loss, but they still find buyers.

Where are you getting the $6m loss from? I can't see anything about it online.