Also, global CC would lower the skillcap and pretty much negate the entire ideas of swaps in Arena. You'd tunnel one target the entire game because if you have CC'd any of the other people, they'd be on DR for stuns which is what most swaps are made with. If the healer you are swapping too isn't stunned, they can just dispel their partners of any CC you might've put them in to swap properly.
Heck, you might not even be able to CC the person you were on to swap because he's on DR from your Kidney/Maim/HoJ/Deep.
It'd be a horrible change.
Maybe putting more CCs together by duration instead of type. 8s Fear should maybe share DR with 8s Poly and Cyclone should maybe share DR with Stuns as they all last 6 seconds (mostly), but Fear shouldn't ever DR Kidney and HoJ shouldn't DR Poly. It'd just be backwards.