It's mostly a case of being irritated that a Sim that has so much good going for it would fall so flat in the one area that virtually every aircraft relies on in one form or another. Also, because after so many years with the poor ATC in FSX and P3D, I find myself wishing I had that system in X-Plane, lol. . .as bad as it is it would be light years ahead of XP.
Draw a design spec sheet for an ATC system that is as detailed as possible and then think about how you would program it and make it run with as little use of resources as possible and maximum flexibility to support as many situations and user configurations as possible as you'll realize that the ATC system in MSFS is - despite its perceived shortcomings - nothing short of a stroke of genius.
There's a reason why ATC is staffed by humans and it's flexibility, which just can't be emulated by AIs (yet).