I say that more coming from dota which pretty much every top team is international. I can understand that for cs the communication needs to be faster, but out side of that i see teams being regional just because. What would make a team like fnatic avoid (example) to go international when swedes speak pretty good english? G2 got international even though jackz english is zywoo levels from what they said.
And yeah, newer mix teams right now are international, but the big ones are still "locked" on this regional stuff.