Where do they put OS X Server and most importantly - why?

Question

macOS

Apple no longer releases servers for its server OS. There used to be Xserve, Mac mini Server, Mac Pro Server ... The current Mac mini and Mac Pro are desktop PCs, although no one forbids installing OS X Server on them, but there is little sense (sorry for the pun) from this. You can’t even put a second disk in the cases of these “poppies”, not to mention the fact that the servers are primarily in data centers, where, as you know without me, you need server cases for rack mounting (we won’t to talk about the fact that in self-made data centers you can at least put an ordinary system unit).
I have no insider information about Apple's infrastructure, but I am more than sure that they have their own servers of one well-known brand and some kind of server OS is running on them (there is a suspicion that this is Darwin, FreeBSD or even RHEL). If this is so, then it’s completely incomprehensible to me why a huge corporation cannot release servers for their needs and install OS X Server on them? ..
PS: While writing these lines, I came across craftsmen from Sonnet Technologies who, in addition to various interesting things, release: xMac mini Server (1U chassis for Mac mini + 2 PCIe slots), RackMac mini (1U chassis for two Mac minis), RackMac Pro (4U chassis for two Mac Pros).

Answer 1

It costs me at work OSX Server on a Mac mini. The thing is absolutely useless. The maximum is to set up the vpn (and it's somehow tricky there) and share the TimeMachine. As for what servers Apple has, I doubt they use OSX. I'm more than sure that they use some kind of Linux distribution. I do not rule out that self-made.