I would suspect that there's a valid reason (probably along the lines of "we are set up to remote manage a bunch of linux and macos machines, and our tools work on them; we don't want to add more overhead") but that the person writing the page didn't entirely understand the reason.

"Mac or linux, but not windows" is a somewhat common policy, or certainly used to be, and it's never about the cost _of the licenses_ (except for tiny companies, perhaps).