I know why, I'm just looking whether or not Gazebo would incorporate an element that prevents City-States from gifting so.In my last game I encountered one weird behaviour, nearly every time a city-state was giving me an unit it was a copy of an UU normally unlocked by decisions. I have been allied with 2 military CS and I got: 5 Mandekalu, 2 Companion, 1 Horseman and 3 Ballista when their associated unique units were Panzer and Winged hussard.
I also noticed quite a few Companion and Mandekalu (2 to 4) present in the armies of other civs. Is there a way to prevent your new units to be gifted by CS (and/or maybe not spawned by barbarians)