Copying some files or recompiling some stuff is not costly, I could believe some compatibility or licensing issues but migration for non-essential software daemons is pretty much a joke thanks to VMs. At the worst you might have some old linked libraries or legacy stuff to worry about. They already have the hardware capacity for other things and they already have to employ people to do this stuff, they don't really save anything significant based on what I see doing IT doing around here and what friends in the industry say.
To be fair though, one legitimate scenario is that there are no more personnel around who have the familiarity with the software and many companies don't want to run it if that's the case. That's happened a few times in the industry and there have been some cases where old server code gets lost in a transition or etc.
But I agree that with 20 players and for the number of years they ran it that this is a fine ending point, especially since the community has an alternative. I just strongly dislike it when companies sunset things and don't let the community who is interested at least run it themselves.
Playing: Dark Souls 2: Scholars of the First Sin Watching: Mr. Robot