I know off the top of my head at least 3 places that would happily purchase a couple of XServers (one of which probably still has one) running MacOS Server. Linux isn't as hard of a requirement as you think.

Hell... I can think of loads of places running servers on WINDOWS (namely all of my employers, including F500 companies) I am not surprised that someone would run macOS as a server. At least MacOS is Unix based ;)