They don't think that at all. They probably know more about Linux than you do because I guarantee half the systems they manage are already running it.
What they think about are the applications that the people who actually make the decisions at your companies refuse to migrate away from. They know the cost of hiring Linux sysadmins vs Windows sysadmins. They think about everyone in every other company and how much harder they are to hire when suddenly none of them know how to use their office computer when they're hired. They think about the half dozen or so business critical applications which genuinely don't have Linux equivalents. None of the executives, nobody in HR, nobody in accounting or business. Nobody in sales. Let alone... nobody in the actual non-tech industry that most businesses operate in.
And it's not the college graduates they're worried about. It's the people with 5, 10, or 15 years experience who will just not want to work at a company where they have to compromise and use non-standard software.
It's still not economically viable for any corporation outside of exactly a small tech industry start-up to switch away from Microsoft, and it has nothing to do with the cost of operating system licenses or support.