I am sure there are tens of thousands if not more. Server admins are very risk averse and don't tend to turn off machines just to check if someone's using it.

I am sure there are tens of thousands if not more. Server admins are very risk averse and don't tend to turn off machines just to check if someone's using it. And in large organizations, it's hard to keep track of who's using what and if they still need it. Imagine working at a hospital or a bank, emailing people about a server, and everyone says it's not being used. Then you turn it off and something critical gets broken at 3am a week later resulting in an emergency. Who gets blamed, you or the people who forgot the server was being used? The people who set it up may not even be working there anymore.