When it's just you, on your own PC, and you don't value your time, it's free.

Just from the license fees here, we're talking what, roughly 2000 employees?

At that scale, you're going to be paying for support. Whether through a third party, or employing enough people to fix all the things that can go wrong. And not everyone in IT knows enough about Linux to fix broken boxes.

I once recommended Linux for our customer servers, to be installed hundreds of miles away. And what I found was that employees who knew Linux (and specifically how to fix it when it fucks up) were more expensive than the trained monkeys we sent out to fix things, who at least knew how to copy data off it and reinstall Windows/slap a new drive in it, and that issues were my fault for recommending it. It was also easier to talk customers through some settings in Windows if it falls off the network somehow, than it was to deal with getting them to type things into a command line.

And that's before you even consider servers and where your stuff all goes. With MS it goes into "the cloud", and you don't need to worry too much about anything other than paying for it. With your own hardware, you very much need to worry because if you don't, then one day it won't be there any more.